The King Kong star, who is now in a relationship with actor Liev Schreiber, romanced Ledger for two years after the couple met on the set of 2003 movie Ned Kelly. They split amicably and remained friends until the actor's untimely death in 2008.
The tragic star was halfway through filming The Imaginarium of Dr. Parnassus when he died, leaving director Terry Gilliam to bring in Colin Farrell, Johnny Depp and Jude Law to complete production as different incarnations of Ledger's character.
The film was released last year (09) - but Watts admits she still still hasn't watched it.
She tells Britain's Marie Claire magazine, "I've always loved Terry Gilliam's films. And Heath was an unbelievably brilliant talent.
"I'm sure he's wonderful to watch. But yeah, it's kind of ... confronting."