Helena Bonham Carter can't remember conceiving her daughter.

The 'Dark Shadows' actress - who has children Billy, eight, and four-year-old Nell with long-term partner Tim Burton - was shocked when she fell pregnant with her youngest child because it came at a time when she and the filmmaker were not getting along during filming of 'Sweeney Todd: The Demon Barber of Fleet Street'.

She said: ''[The film was] the nadir of our professional relationship but somehow we managed to conceive a daughter.

''[I'm amazed we had Nell] because you have to have sex to get pregnant don't you?

''[We must have had sex] but that's what I can't remember. No, we did do it once.''

The 45-year-old beauty returned to work just 12 weeks after giving birth to Nell - but had to wear ''nappies'' because the physicality demanded by her role of Bellatrix Lestrange in 'Harry Potter and the Deathly Hallows' was too much for her weak pelvic floor muscles.

She explained to Style magazine: ''I really couldn't jump up and down and scream without losing most of my bodily liquid. They had these air dryers, these huge things - that's where I would try myself off.

''[I eventually wore] nappies. None of the men noticed. They don't know, you see. But all the girls were like, 'How can you?' But actually, I don't think I was too embarrassed.''