Michael Caine was seriously concerned for Heath Ledger's well-being

Movie legend Michael Caine has admitted he was seriously concerned for Heath Ledger's well-being months before his death.

'Alfie' star Caine, 74, worked with tragic Heath on the Batman movie 'Dark Knight' late last year and could tell he was "exhausted" all the time.

Heath eventually died in January after of "acute intoxication from the "abuse of prescription medications" - many believed to be due to chronic insomnia.

"He was exhausted, I mean he was really tired," Caine admitted of their filming time together. "I remember saying to him, 'I'm too old to have the bloody energy to play that part.'

"And I thought to myself, I didn't have the energy when I was his age."

There has been growing concern that Heath's portrayal of the Joker - basing it part on Sex Pistols wild man Johnny Rotten, part on Malcolm McDowell's maniac in 'A Clockwork Orange' - may have thrown him over the edge.

Wally Pfister, the cinematographer on Dark Knight, admitted that the star "seemed "like he was busting blood vessels in his head" he was so intense.

"It was like a s?ance, where the medium takes on another person and then is so completely drained," he added.

Director Christopher Nolan believes Heath's "terrifying, amazing" performance will go down in Hollywood history.

"It's stunning, it's iconic," he said. "It's going to just blow people away."