Del. Code tit. 12, § 1542

If, after the grant of letters testamentary or the grant of letters of administration, a will of the deceased is admitted to probate and letters testamentary or of administration with the will annexed are thereupon granted, the prior executor or administrator shall by such grant be removed from office. All the previous lawful acts of the removed executor or administrator shall be valid as provided in § 1545 of this title.