Naomi Watts has paid tribute to her former partner Heath Ledger on what would have been his 39th birthday.

The 49-year-old actress was in a relationship with the late actor - who passed away in 2008 from an accidental intoxication from prescription drugs - from 2002 to 2004, and has taken to Instagram to mark what would have been the 'Dark Knight' star's special day.

Alongside a professional picture of the pair of them at a red carpet event, Naomi wrote: ''Happy birthday to this darling heart. We will never forget you... #heathledger #rip (sic)''

This isn't the first time the 'Gypsy' actress - who has Alexander, 10, and Samuel, nine, with her ex-husband Liev Schreiber - has paid tribute to Heath either, as she previously took to social media to mark the 10th anniversary of his passing in January this year.

Posting a professional snap of Heath - who went on to date Michelle Williams, with whom he had a daughter named Matilda, now 12 - Naomi wrote: ''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. (sic)''

Previously, Michelle insisted it ''won't ever be right'' for her to raise Matilda - who was just two at the time of Heath's passing - without her father.

She said: ''In all honesty, for pretty much everything else, I feel like I'm a believer in not fighting circumstances, accepting where you are and where you've been.

''In pretty much all senses but one, I would be able to go totally down that line of thinking were it not for Matilda not have her dad.

''You know, that's just that something doesn't ... I mean, it just won't ever be right.''