Appointment of guardian ad litem.) When an heir or legatee of a testator is a minor or person with a disability who is entitled to notice under Section 6-10 at the time an order is entered admitting or denying admission of a will to probate or who is entitled to notice under Section 6-20 or 6-21 of the hearing on the petition to admit the will, the court may appoint a guardian ad litem to protect the interests of the ward with respect to the admission or denial, or to represent the ward at the hearing, if the court finds that (a) the interests of the ward are not adequately represented by a personal fiduciary acting or designated to act pursuant to Section 28-3 or by another party having a substantially identical interest in the proceedings and the ward is not represented by a guardian of his estate and (b) the appointment of a guardian ad litem is necessary to protect the ward’s interests.