On August 5, 1972, Duke married actor John Astin, after having been in a relationship with him for two years. When the wedding guests were invited to speak, 18-month-old Sean looked at John and cried, "Daddy!", to which the Episcopal priest performing the ceremony remarked, "Well, that about does it!" Astin subsequently adopted Sean. In 1973, Duke gave birth to Astin's brother, Mackenzie Astin, who also became an actor. Duke and John Astin divorced in 1985. Duke married Mike Pearce in 1986, and they adopted a son, Kevin, in 1989.