The actress, who dated The Dark Knight star from 2002 to 2004, shared a photo of the two holding hands as they walked down a red carpet together.
“Happy birthday to this darling heart,” she wrote on her Instagram Wednesday. “We will never forget you.”
“Thinking about this beautiful soul today. 10 years ago he left this world. He was a true original,” she wrote at the time. “Heart always on his sleeve, with the most powerful charisma, strength, humor and talent. I will never forget his gentle spirit.”
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Following their split, Ledger dated Michelle Williams after meeting on the set of their 2005 film Brokeback Mountain and welcomed their daughter Matilda in October 2005. They separated in September 2007.
Ledger was found dead on Jan. 22, 2008 in his apartment. He was 28. A toxicology report revealed a fatal mix of prescription drugs in his system. Ledger was survived by his partner at the time, Williams, and his only child, Matilda (now 12).