It's hard to believe, but it's been ten years since actor Heath Ledger unexpectedly died on January 22, 2008.

The Australian actor, who was found unconscious in his Manhattan apartment, died from a cardiac arrest caused by an acute intoxication by a combination of prescription medication and sleeping pills.

Actress Michelle Williams, the Dark Knight star's ex-girlfriend and the mother of his daughter, Matilda, released a statement shortly after the news of his demise broke.

"Please respect our need to grieve privately," said Michelle. "My heart is broken. I am the mother of the most tender-hearted, high-spirited, beautiful little girl who is the spitting image of her father. All that I can cling to is his presence inside her that reveals itself every day. His family and I watch Matilda as she whispers to trees, hugs animals, and takes steps two at a time, and we know that he is with us still. She will be brought up in the best memories of him."

Tributes from other celebrities and fans also began to pour in, and many people have since taken the time to honor Ledger's memory each year on the anniversary of his death.

This year, one of Ledger's former flames, actress Naomi Watts, is also making sure that the actor's memory lives on. Watts, 49, who dated Ledger for two years, from 2002 to 2004, took to Instagram to share a photo and heartfelt message.

Watts shared a black and white photo of Ledger on the social media platform, along with a caption that read:

"Thinking about this beautiful soul today. 10 years ago he left this world. He was a true original. Heart always on his sleeve, with the most powerful charisma, strength, humor and talent. I will never forget his gentle spirit. ❤️ #heathledger"

This isn't the first time that the 21 Grams star has opened up about being close with the late actor. In 2011, she told More magazine that Ledger was a "special soul and made a great impact on my life."

"We had a beautiful relationship, only a couple of years, but he was a man who was completely full of joy, and there was a lot of laughing and affection," Watts said.

The actress isn't the only celebrity in Hollywood who has spoken about the impact Ledger has had on their life. Back in 2015, his Brokeback Mountain co-star Jake Gyllenhaal also got candid about losing Ledger.

"I think losing Heath and being a part of a family that was something like the movie, the movie we all made together, makes you see that, makes you appreciate that and hopefully moves you away from the things that really don't matter to the things that do," he told NPR. "I'm trying to have relationships that are as real as they possibly can be on a movie set, be close to people because I know that it's precious."

In addition to all the tributes, Ledger's memory was immortalized in a documentary titled I Am Health Ledger. Filmmaker Derik Murray explores Ledger's rise in Hollywood, from 10 Things I Hate About You to The Dark Knight, and shows an intimate side of the actor that many did not see when he was alive.

Ledger's memory also lives on through his 11-year-old daughter, who apparently has her father's energy. She has been occasionally spotted on outings alongside her mother, and the resemblance to her father is uncanny.

"She's got his energy," Kim, Ledger's father told Australia's Channel 10 in 2015. "Heath never slept from when he was two and Matilda's like that. She's just got this ball of energy and she radiates this little aura."

It's safe to say that Ledger will not be forgotten anytime soon.