United Kingdom, Feb. 24 -- Hilary Duff's "heart aches" for her former Lizzie McGuire co-star Robert Carradine.

Robert - who played Hilary's onscreen dad Sam McGuire in the hit Disney teen show - has died aged 71 with his brother Keith Carradine confirming his sibling took his own life after a "nearly two-decade battle with bipolar disorder", a mental health condition which leads to extreme mood changes, and Hilary has now shared her heartache after hearing the sad news.

In a post on Instagram, she wrote: "This one hurts. It's really hard to face this reality about an old friend.

"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 ...