Ledger is not what you'd call Hollywood-groomed - he's more Johnny Depp than Tom Cruise - and he's clearly doing everything he can to play down his otherwise dangerously disarming face. He's a reluctant heart-throb, which is unfortunate as when we meet Los Angeles is plastered with larger-than-life posters of his face to advertise his latest film, A Knight's Tale.
It's made in the style of Baz Luhrmann's Romeo and Juliet (the film that made Leonardo Di Caprio a star) and stars Heath as 14th century William, the son of a thatcher who harbours dreams of becoming a jouster. Only knighted aristocrats are permitted to joust, so when an opportunity to sidestep the rules comes up, William's not going to ignore it - so it's bye-bye William, hello Sir Ulrich. And hello, Heath....
'It was a lot of fun. I don't know what it would have been like in Prague as a tourist - I guess, very touristy! - but certainly it's great to work there. Socially, you know, we had such a tight-knit little community. You could just walk to each other's houses and go for breakfast, or lunch.'
You had your own house there?
'Yeah, most of us just went out and rented a house. Well, we didn't really have time, they (the studio) just sent someone out there to get us houses!'
The film's soundtrack is classic rock. Is that your kind of music?
'Yeah, can you believe it? I absolutely love all the music in the film!'
That's funny 'cos I hear you play the didgeridoo. How long has that been a hobby?
'Six years. It's kind of a good luck thing - I usually take it to my sets. Brian Helgeland, the director of A Knight's Tale, wanted me to play it in the film. I didn't, though. He also wanted me to use a real thick Australian accent! Then he said I could have whatever accent I wanted, so that's why I have a kind of an English one.'
Julia Stiles, who played Katarina in your previous hit film Ten Things I Hate About You, has described you as 'eccentric'. What did she mean?
'I don't know (laughs). You should ask her that, I guess. It's a little hard to say....'
Why do you think Australians are making such big waves in Hollywood right now?
'I kinda feel that, to some degree, Australians are in fashion right now. I think it's seasonal, but then we do bring different flavours to what we do. An Italian filmaker can bring romanticism to film because of where he's from. I guess there's something that we Aussies have that we bring, too. I don't know what it is, though. The humour, the barbeques, the sunshine, the attitude, the beer, you know? So I guess that's it.'
How big a star are you currently in Australia?
'Going home is really weird because in Australia it's a bigger deal. And also because I only get to go back there every six months, I only see life there change in leaps and bounds. It's like six monthson, boom, lots has changed. Ultimately, though, my family and friends stay the same.'