Before meeting him, all I know about Michael Rooney is that his father is former child star Mickey Rooney and that he choreographed one of the best pop videos of the last five years: Kylie Minogue's Can't Get You Out of My Head. He hasn't given many interviews. As we settle backstage at the Albery Theatre, where Rooney is choreographing a new musical, Ducktastic!, I confess that I haven't even been able to find out which of his father's seven wives is his mother.

"Oh, don't worry," he says, waving a hand in a this-happens-all-the-time gesture. Rooney is buffed and bronzed and looks, at 43, like he has never knowingly swallowed a toxin. He was born and bred in Los Angeles. "My mother was Barbara Thomason, number five on his list. She was an aspiring actress. She is no longer with us."

Oh, I'm sorry.

"Yuh," he says. "What happened was - the story is kind of intense: my mother was murdered."

God. I'm sorry.

"I don't remember a thing. I was about three or four. And my mum and my dad were going through a divorce. My mum was kind of seeing somebody on the side. But then my father and my mother decided to get back together, and the guy my mum was dating wasn't having it. So he took the very gun that my father gave my mother for protection and killed her in our house. Then killed himself. It was a murder suicide."

There is a stunned silence.

"So. It was very intense."

Christ.

He sighs. "We were in the house when it happened. But I don't remember a thing. We were scurried out and told we were going to see the movie Mary Poppins. It wasn't like, oh, your mother's dead upstairs."

Rooney hasn't said this glibly. But his disregard for the inhibitions of interview is extraordinary. All my questions about Ducktastic! and its director, Kenneth Branagh, fly out the window. I ask what happened next.

"Well, my father was going through a tough time in the 1960s, so my grandparents adopted us, my mother's parents. It was stable after that."

He says that if he seems adjusted about it (like, "yeah"), it's because his grandparents lived completely sane and un-showbizzy lives and he had limited contact with his father. "My grandparents taught me to rake the leaves in the backyard, clean up my room, all that stuff. And we went to regular schools."

His mother had three other children with Mickey Rooney, and all four of them were brought up by their maternal grandparents. Rooney got into choreography after a school production of West Side Story and, after years of training as a dancer, got his first job as an extra on the television series Fame. I ask him at what age he found out what happened to his mother.

"I think I was about 13 or 14. That's when I really understood what had happened. For years I thought my grandmother was my mother, because the transition was so smooth. And then my grandmother sat us down and told us why our mother was no longer around. She started showing us pictures of my mother. The way they did it was really good."

None of Rooney's sisters went into showbusiness. Two are hairdressers, one a dental technician. He has a further six half-siblings from his father's other marriages, one of whom was to Ava Gardner ("I know," he says, rolling his eyes, "can you believe it?), which didn't produce children.

"Let me see now: all in there's Timmy, Teddy and Mickey Jr. There's Jimmy and Jonelle. Then there's Kelly, Kerry and Kimmy and my father calls me Kyle, so we kind of all match."

He has his father's full-moon face. Mickey Rooney is now 85 and married to his seventh wife, Jan Chamberlain, with whom he has been for 25 years. She has "really calmed him down". I can't imagine what sort of a father he would be; in popular memory he's always that grinning teenager, threatening to "put on the show right here".

Rooney sighs. "Up until 10 years ago, showbusiness was all he talked about. We'd be at the table and I'd say, I love that couch. And he'd say, 'Oh, that couch, that reminds me of when I did this movie.' He always feels like there's a camera in front of him or a spotlight and he is number one. Less so now."

This must have been difficult.

"Yeah. There were times when I would dread going over to his house. But he didn't know what else there was to talk about; that was the only life he'd known. You know, my father was shooting two to three musicals at the same time when he was a kid. They were cranking 'em out back then. They used to put stuff in the soup to keep 'em going - everybody says it was cocaine - anyway, it was some kind of upper. But he's a survivor, unlike poor Judy [Garland, with whom he worked]."

Her kids didn't fare so well, I say.

"I know. Thank God I didn't turn out like Liza, right?"

Did Rooney ever talk to his father about his mother's murder?

"He doesn't like talking about it at all. But we've talked a couple of times. He told me that my mother was one of the most wonderful ladies he had ever met, that she was really nice, a caring person, she was wonderful with us and loved us all. At that point, I really needed to hear that."

In the past three or four years, says Rooney, he and his sisters have been thinking about looking up the press cuttings and police reports from the time of their mother's murder. "I think I can handle it now," he says. When I get back to the office, I look it up too; it happened in 1966; her lover's name was Milos Milocevic

· Ducktastic! is at the Albery Theatre, London WC2. Box office: 0870 950 0920.