Lara Spencer is a doting mother to two teenage children, and was feeling extra proud of her son Duff over the weekend.MORE: Lara Spencer makes plea for help after making discovery at family homeThe Good Morning America star attended the teenager's school graduation, and shared a heartfelt tribute to him following his milestone moment.Alongside a picture of Duff smartly dressed in a suit while collecting his award, she wrote: "One more—because I just can’t believe he’s a graduate. VIDEO: GMA's