Naomi Watts and Heath Ledger dated from 2002 until 2004.

Hollywood star Naomi Watts has revealed it was a "very sad day" when she learned of the death of Heath Ledger, her ex-boyfriend.

The 48-year-old actress dated the Hollywood star - who died of an accidental overdose of prescription drugs in 2008, aged 28 - from 2002 until 2004 and she's confessed to having been shaken by his sudden death.

Reflecting on his passing, Naomi shared: "That was a very sad day."

Naomi's comments feature in a soon-to-be-aired documentary about Heath's life on Channel Seven in Australia.

The production also features interviews with Heath's family and friends, in addition to hours of home video shot by the 'Dark Knight' actor.

Although she was no longer dating Heath at the time of his death, Naomi is visibly emotional in the preview clip and has previously confessed she has nothing but fond memories of her time with her ex-boyfriend.

In 2011, she explained: "He was really a very special soul and made a great impact on my life.

"And a great actor, but I know there was so much more to come. And it's such a tragedy for his little daughter."

Earlier this year, Heath's father Kim Ledger insisted that he and his family can still feel the late star's presence.

Kim said: "He gave us a lot of love as an individual, he was an amazing young guy.

"He loved his family and his friends and we loved him right back. We still feel like he's around us every single day."

Since his son's passing, Kim has also called for tighter monitoring of prescription medications, to prevent similar tragedies.

He previously said: "The addiction to prescription drugs is a massive problem.

"I think from a government point of view it would be great to see real-time monitoring systems in each country."