Helena Bonham Carter and Tim Burton are too ''lazy'' to get married.
The couple - who have been together 11 years and have children Billy, eight, and four-year-old Nell - famously live in adjoining houses because they need space from one another, though the actress insists this doesn't mean their relationship isn't serious.
She said: ''We're not [married], actually. Not through any kind of ... Through laziness, really.
''Our houses are married. It is very good to have. You definitely need your space.''
Helena and Tim have worked on seven movies together and the 45-year-old actress thinks it is important that she gets to see him work otherwise she would worry about the filmmaker's stress levels and unhappiness when he came home in the evenings.
Speaking to Daniel Radcliffe for Interview magazine, she said: ''He is very stressed. Directors are. The stress level - it's a battle. I mean everything that can go wrong goes wrong.
''But then again, what's great about working with Tim - when you're involved with him - is that I get to see that on set, he's having fun. But if I didn't get to go on set, I'd think he was suicidal for six months.
''I love seeing him work. It's a really good thing. It's very healthy to do, every so often.''
The 'Dark Shadows' star insists she would be ''insane'' if she turned down any roles she is offered by Tim because she thinks he is a ''genius'', though there are also practical reasons for their frequent collaborations.
She explained: ''It makes sense for me. I've got two children with the man. It doesn't make any sense to be going around the other side of the world and doing some other thing.
''It's Tim Burton. He's a genius. You can't turn him down just because you go out with him and have two children together. It would be insane. It would be positively wrong, and stupid.''