In an Instagram post on Tuesday, the 51-year-old actress shared rare photos with the star, who was found dead on Jan. 22, 2008 in New York City, at age 28.
"Going through my photos I found these. Just remembering this time. Heath Ledger was such a special person," the Boogie Nights star wrote alongside the pictures.
In two of the snaps, Graham and Ledger can be seen snuggled up to one another. The last shot showed The Dark Knight actor taking a mirror selfie.
The former couple dated briefly from October 2000 to June 2001. A rep for Graham confirmed that the stars were "still good friends" after their split, according to IMdb.
Ledger later went on to date his Brokeback Mountain costar Michelle Williams after they met on set in 2004. The couple welcomed their daughter, Matilda (now 15), in 2005 but called it quits in 2007. Five months later, the actor died of a prescription-drug overdose.
In 2018, Williams opened up about raising her now-teenage daughter without Ledger in an interview with Vanity Fair.
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"I always say to Matilda, 'Your dad loved me before anybody thought I was talented, or pretty, or had nice clothes,' " Williams, 40, said at the time.
"When you're a single parent, and that element of provider and protection is missing, it's scary," the Blue Valentine star said.
Michelle Williams went on to wed musician Phil Elverum in 2018 with the couple splitting in 2019. She remarried in 2020 to theater director Thomas Kail.