¶1While hospitalized shortly before his death in November of 2004, George R. Girard (George) executed a last will and testament to replace his previous will, executed in 1983. At the time of his death, the most valuable asset in George’s estate was thought to be the anticipated proceeds from a lawsuit he had filed seeking damages for personal injuries suffered from his exposure to asbestos.
¶2Background. George and Theresa married in 1971. In 1983, George executed a will that left his entire estate to Theresa outright, if she survived him.
¶3In May 2004, George was diagnosed with stage IV mesothelioma, a deadly form of lung cancer that can be caused by ex*411posure to asbestos. After receiving that diagnosis, George hired an attorney from Connecticut (whom Alan introduced to him) to initiate a lawsuit for his injuries from asbestos exposure. The attorney informed him that the suit could yield a significant settlement or judgment, possibly exceeding one million dollars. George discussed with Alan his wish to direct the proceeds of any such settlement or judgment to a trust for the benefit of Theresa during her life, with any trust assets remaining upon her death to be distributed in equal amounts of up to $10,000 to each of Alan and Paula’s four children, and any amount remaining after those distributions to be divided between Paula (sixty-five percent) and her brother Anthony MacWilliams (thirty-five percent).
¶4At George’s request, Alan (by electronic mail [e-mail], on November 5, 2004) contacted Attorney Scott Fenton of Bowditch & Dewey, a Worcester law firm that had previously represented Alan and Paula in a variety of personal and business matters, to prepare an estate plan with provisions for the anticipated proceeds from the lawsuit. Alan conducted all communications with Bowditch & Dewey concerning George’s estate plan, initially with Fenton and later with Attorney Maryjo Hart (who prepared the estate planning documents). On November 10, 2004, Alan sent an e-mail to Fenton asking whether the documents were ready for signature, explaining that “George is going fast and I want him to sign.” The November 10 e-mail furnished further instructions regarding the trust established for the proceeds from the asbestos lawsuit: “Paula Germain shall controll [sic] the trust and have full say in how the money is used to take care of George and Theresa Girard. Upon the death of George and Theresa the trust shall be liquidated and [thirty-five percent] goes to Anthony MacWilliams and the remainder to Paula Germain of course after the trust has paid all debts.”
¶5A short time thereafter, during the early morning hours of *412November 12, 2004, George became extremely short of breath and was taken to the hospital by ambulance. He was stabilized with oxygen, morphine, steroids, and antibiotics. Between 10:00 and 11:00 that morning, Attorney Hart arrived at the emergency room with the completed estate planning documents.
¶6On July 14, 2005, Theresa filed a petition to probate George’s 1983 will. Paula entered an appearance in that action and filed an affidavit of objections. On or about August 23, 2005, Theresa filed a verified equity complaint seeking to have the 2004 will and related trust documents declared null and void. On September 2, 2005, Paula filed a petition to probate George’s 2004 will.
¶7The petitions for the probate of the two wills were tried by a probate judge over a period of six days in 2006. The judge entered extensive findings of fact and concluded that the 2004 will was not the product of undue influence. A judgment entered approving and allowing the 2004 will as the final will of George R. Girard. Two separate judgments entered dismissing (1) Theresa’s petition for probate of the 1983 will and (2) Theresa’s August 23, 2005, complaint in equity. Theresa filed a notice of appeal from the judgment approving the 2004 will as George’s last will and testament.
¶8Discussion. “In a will contest involving allegations of undue influence, the burden of proof ordinarily rests with the party contesting the will.” Estate of Moretti, 69 Mass. App. Ct. 642, 651 (2007), citing Tarricone v. Cummings, 340 Mass. 758, 762 (1960). However, in cases involving a fiduciary, “the fiduciary who benefits in a transaction with the person for whom he is a fiduciary bears the burden of establishing that the transaction *413did not violate his obligations.” Clearyv. Cleary, 427 Mass, at 295.
¶9“Although some fiduciary relationships, such as that between guardian and ward, are created by law, others arise from the nature of the parties’ interactions. The ‘circumstances which may create a fiduciary relationship are so varied that it would be unwise to attempt the formulation of any comprehensive definition that could be uniformly applied in every case.’ ” Doe v. Harbor Schs., Inc., 446 Mass. 245, 252 (2006), quoting from Warsofsky v. Sherman, 326 Mass. 290, 292 (1950). “Where the fiduciary relationship is not one created by law, the existence of the relationship ordinarily is a mixed question of law and fact for which the party asserting the relationship bears the burden.” Ibid.Though the trial judge did not address Theresa’s argument that Alan was a fiduciary in fact, if not by strict formal arrangement, the judge’s subsidiary findings leave no doubt that Alan stood in a fiduciary capacity toward George in the preparation of George’s 2004 will and related documents. The judge found that George placed his trust and confidence in Alan, based upon a close relationship over ten years. George trusted Alan to manage his household affairs and expenses while George and Theresa were in Florida for significant portions of the year. Of even greater significance with reference to the present case, George entrusted to Alan all responsibility for overseeing the preparation of his 2004 will and related documents, and George’s deteriorating health left him wholly dependent on Alan’s assistance toward that end.
¶10There is likewise no doubt that Alan stood to benefit from the transaction in which he was involved. Though Alan was not named a beneficiary under the will or the trust, his wife, Paula, was. Under the principles enunciated in Clearyv. Cleary, supra,his status as a fiduciary subjects his actions to heightened scrutiny. *414Though Alan was not a party to the petition (by reason of the fact that he was not a beneficiary under the will), in circumstances where a fiduciary stands to receive a benefit indirectly we see no reason why the burden shifting prescribed by Clearyv. Clearyshould not be applied to the direct beneficiary (here Paula) from whom the fiduciary’s (here Alan’s) indirect benefit derives. Accordingly, under Clearyv. Cleary, supra,the judge should have placed on Paula the burden of establishing that Alan did not exert undue influence on George in connection with the 2004 will and trust.
¶11“Four considerations are usually present in a case of undue influence: ‘that an (1) unnatural disposition has been made (2) by a person susceptible to undue influence to the advantage of someone (3) with an opportunity to exercise undue influence and (4) who in fact has used that opportunity to procure the contested disposition through improper means.’ ” O’Rourke v. Hunter, 446 Mass. 814, 828 (2006), quoting from Tetrault v. Mahoney, Hawkes & Goldings, 425 Mass. 456, 464 (1997). There was evidence in the record that would enable a rational trier of fact to find that each of the four considerations was present. Though the trust expressly provided that its purpose was to ensure that Theresa’s needs were met during her lifetime, it vested exclusive discretion in Paula, as trustee, over the amounts, purposes, and timing of payments from the trust. Though Theresa was somewhat unsophisticated in financial matters, there is no indication in the record that she was a spendthrift. The judge’s findings furnish no explanation why the imposition of a trust, vesting sole discretion in Paula over distributions, was necessary or appropriate to achieve George’s stated objectives, in contrast to the terms of his 1983 will (which devised his entire estate to Theresa outright), or in contrast to a trust that gave Theresa the right to demand distributions from time to time.
¶12Because the trial judge placed the burden of proof on the wrong party, and because there was evidence to support a contrary conclusion, his conclusion that there was no undue influence cannot stand.
¶13Other issues. We address briefly Theresa’s other claims of error. First, Theresa cannot sustain her claim that the judge erred in refusing to allow Dr. Howard Sachs to offer his opinion regarding George’s testamentary capacity to execute the 2004 will and related documents, because she made no offer of proof at trial to indicate what his testimony would have been. Absent an offer of proof, she cannot demonstrate that she suffered any prejudice as a result of the challenged evidentiary ruling. See W.A. Robinson, Inc. v. Burke, 327 Mass. 670, 677 (1951); Commonwealth v. Blake, 409 Mass. 146, 158-159 (1991); Brodin & Avery, Massachusetts Evidence § 1.3.4. (8th ed. 2007). Her contention that the judge erred in finding that George possessed testamentary capacity fails as well; to the extent the contention rests on her assertion that Dr. Sachs’s excluded testimony would have dictated a contrary conclusion, it rests on speculation (in the absence of an offer of proof) concerning what his testimony would have been.
¶14Conclusion. The judgment is vacated, and the case is remanded to the Probate and Family Court for further proceedings consistent with this opinion.
¶15So ordered.
¶16during his life, George had worked as a carpenter, exposing him to asbestos. In May 2004, he was diagnosed with a form of cancer that can be caused by asbestos exposure.
¶17Theresa was George’s second wife, and they had no children together. Paula is Theresa’s daughter from a previous marriage. Theresa had two additional children from the previous marriage. George had four children from a previous marriage.
¶18If Theresa predeceased him, the 1983 will devised George’s annuity fund and benefits to his children, and his real estate and other assets to Theresa’s children.
¶19Gifts included money, a new car, and renovations to the couple’s Upton home.
¶20A third sibling, Carol Stockton, was to take nothing under the trust.
¶21The documents included wills for George and Theresa, durable powers of attorney and health care proxies for George and Theresa, and the trust described above.
¶22Alan had previously informed Hart that George was “too sick” to speak with her over the telephone. The record does not indicate whether Hart asked to communicate directly with Theresa.
¶23A narrow exception to the Clearyrule arises in circumstances where the fiduciary has not taken part in the questioned transaction. See Rempelakis v. Russell, 65 Mass. App. Ct. 557,563 (2006). In imposing the burden of establishing undue influence on Theresa, the trial judge relied on Rempelakis, noting that Paula played no active role in preparing George’s 2004 estate-planning documents. The judge appears to have considered Paula a fiduciary by virtue of her designation as trustee of the trust established to receive the anticipated proceeds of the asbestos suit.
¶24Though the judge found that the 2004 estate planning documents were designed to minimize tax consequences, the judge conducted no analysis of why the particular structure was chosen, or whether or how it accomplished the objective of tax avoidance. For example, he conducted no analysis whether a trust was necessary (based on the anticipated size of George’s estate), in order to achieve the desired tax savings, or whether the trust needed to vest exclusive discretion over distributions in Paula. Moreover, the judge’s find*415ings are silent on whether the sought-after tax savings would occur in the probate of George’s estate, or later, upon Theresa’s death.