(a) If the court terminates the parent-child relationship with respect to both parents or to the only living parent, the court shall appoint a suitable, competent adult, the Department of Family and Protective Services, or a licensed child-placing agency as managing conservator of the child. An agency designated managing conservator in an unrevoked or irrevocable affidavit of relinquishment shall be appointed managing conservator.
(b) The order of appointment may refer to the docket number of the suit and need not refer to the parties nor be accompanied by any other papers in the record.