Actress Kate Bosworth and many other Heath Ledger fans were quick to take to social media to post tributes of the late Australian actor, who would be celebrating his 40th birthday Thursday.

Bosworth posted a lengthy Instagram tribute to Ledger, whom she called "sensitive, gentle, kind [and] wickedly funny."

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"Doesn’t seem so long ago we were all running around LA, shotgunned into Hollywood + popping off the new millennium’s cork, having a laugh. It was a crazy time. I was literally straight out of high school, feeling young & super shy and he was always so sweet within a surreal scene. I really, really would have loved to have known Heath today, at 40. No limits on what he would have accomplished. Here is what I remember: he was sensitive, gentle, kind, wickedly funny," she wrote, in part.

"Gone too soon. What a talent. That will love [sic] on. As will his sweet daughter," actress Rita Wilson commented in response, referring to Ledger's now 13-year-old daughter Matilda, whom he shares with actress Michelle Williams.

"You are so eloquently spoken. Thankful you share your words with us," one fan also said in response.

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On Twitter, many made references to Ledger’s role as the Joker in the 2008 thriller “The Dark Knight.” The role was the actor’s last before his death.

“Happy birthday Heath Ledger -- the greatest villain this world has ever seen! Gone but never forgotten,” one fan wrote on Twitter.

“Remembering this amazing man on his 40th birthday. Happy Birthday Heath Ledger, you'll always be in our hearts,” another said.

"Today is the legendary Heath Ledger's birthday. A man whose impact can't be understated and whose legacy will never be forgotten. He gave us an instantly iconic portrayal of The Joker that remains the gold standard in villainous performances. RIP Heath,” said a third.

“He would’ve been 40 today. He was one of the best actors and best people that Hollywood will ever see. I miss you so much and just know that we still remember you down here. RIP. Happy birthday Heath Ledger,” a fan shared.

“Happy 40th Birthday to Heath Ledger. An inspiration to me and so many. Such an incredible human that I hold so close to my heart. You are missed each day,” another wrote.

Ledger was found dead on Jan. 22, 2008 in a New York City apartment. It was later determined he died of an accidental prescription pill overdose. He was 28.