Heath Ledger at heart of last film 

Source: Reuters'Heat', an oil on canvas portrait of Heath Ledger, painted shortly before he died by artist Vincent Fantauzzo

Heath Ledger's spirit lives on in his final film, director Terry Gilliam says.

The Imaginarium of Doctor Parnassus is due for release in the UK on October 16 and Gilliam says the late Australian star, who died in January 2008, would have wanted the movie finished.

"Heath had been running full pelt, carrying the whole film on his shoulders. Telling me what to do; insatiable, exhausting," Gilliam told The Observer.

"The thing about Heath was that he was all positive," Gilliam added.

"There wasn't a darkness about him and we had to hold on to that. It eased the grief in a way. Because even after he died we were still working with him every day ... I think it is important that we got it done. Heath would have wanted to see it finished."

Gilliam said when he first heard of Ledger's death, he didn't know how he could continue with the project.

Only two-thirds of Ledger's role had been filmed and investors began pulling out the morning after news of his death broke.

"You can't believe how quickly the money ran away from this thing," Gilliam said.

It was Gilliam's 31-year-old daughter, Amy, working for the first time as a producer, who convinced him the film could be completed.

Ledger's friend Johnny Depp filled some of the remaining scenes, while Jude Law and Colin Farrell covered the rest and Gilliam rewrote the script to include the capacity for shape-shifting within the character.

Gilliam also had to deal with his emotional trauma over Ledger's death in New York from an accidental overdose of prescription drugs at the age of just 28.

He said he was helped by a meeting with the actor's family, during which they cried and laughed while sharing stories and memories of the star, who won a posthumous Oscar for his role as the Joker in The Dark Knight.

"He was so strong," Gilliam said.

"That's why none of it makes sense. The last night before he died we were shooting in Clerkenwell in London, this scene where Dr Parnassus's wagon collapses.

"The last piece of film of Heath is of him holding on for dear life to the back of a runaway travelling theatre. What a way to go! He was doing everything that night, all his own stunts. You really felt as a director there was nothing he wasn't capable of."