Dolly Parton says the secret to her 50-year marriage is distance.

The 70-year-old singer tied the knot with Carl Thomas Dean in 1966 and joked that being on the road for her career has helped their marriage to survive.

Asked for the secret to making a marriage last, Dolly told Vanity Fair: ''Yeah, stay gone! We've been married for 50 years and I've been gone for about 47 of those. But the truth is, we've always been very compatible. To those that follow the signs, I'm a Capricorn and he's Cancer, and those are very compatible signs. But we've always had a good time together, and he's got a great sense of humour and so do I. And he loves staying home and I love staying gone, so it's worked out really well.''

Dolly also revealed her belief that the couple have become even more compatible as they have gotten older.

She said: ''Well, it's just grown deeper. The longer you live with somebody, the more you know them, and you take on all their traits as well as them taking all of yours. And you just have a deeper and better understanding - more of an appreciation. But we've always had a great respect for each other, and I think that's been the thing that really and truly sustained us through the years.''

Meanwhile, Dolly revealed that her song 'I'm Sixteen' was inspired by her sister, who found love again after a ''couple of really bad marriages''.

She said: ''I kind of patterned that after one of my sisters that had had a couple of really bad marriages, brokenhearted, and felt she'd never love again and felt it just wasn't meant to be. But she found someone! And they both had had broken marriages. And they're just like little teenagers and I just get such a kick out of watching them. I thought, 'God, they think they're 16!' And so that's really where I got the idea of writing that song.''