Article continues below advertisementHilary Duff is grieving the loss of her Lizzie McGuire costar Robert Carradine, who died at age 71 after a battle with bipolar disorder. "This one hurts. It's really hard to face this reality about an old friend," Duff, 38, wrote via Instagram on Tuesday, February 24, alongside throwback photos with her former on-screen dad. "There was so much warmth in the McGuire family and I always felt so cared for by my on-screen parents. I'll be forever grateful for that. I'm deeply sad to learn Bobby was suffering.