Now I'm a writer. I'm just finishing a novel. and I've got another one that's going to be a TV series in America. Perhaps David will play a role in it, who knows? We haven't really talked about it.
David's first experience of acting was in 1967 when he came to watch the premiere of one of my plays, which was on Broadway.
In the play, the lead actor sits on a chair and stays there for three hours. David watched from the wings and was fascinated by just one thing -- how can an actor stay there all that time without going to the toilet?
He was obsessed. It's all he wondered about. He thought it would be fantastic to be on stage, but I wouldn't say that's when he decided to become an actor. That came very late.
He got an honours degree at Princeton University, then went on to do his Masters at Yale. As he wanted to make some money, someone suggested he model. At the model agency, someone suggested he took acting lessons. He did, liked it and said goodbye to his studies.
I wasn't disappointed. I thought he'd find academic life too narrow.
The ivory tower that university lecturers live in wasn't for him. But his mother was furious that he'd given up studying.
Even now, when she speaks to him on the phone, she always asks him: "When are you going to finish your thesis?" It makes him laugh. He says: "Later, later."
David was born in New York, grew up in Manhattan and I lived with him until he was 12 when his mother and I split up.
He was a very bright kid with a brilliant sense of humour.
I remember the first chat I had with his teacher when David was six.
He said David was the one who smoothed things out for all the other children. If there was a fight, he'd intervene and sort it out.
These days I'd compare him with Harrison Ford. David's got a very soft personality; he feels at ease with people.
As a child, he talked the whole time. His brother, who's three years older, would say: "He never stops, with all these questions."
At school he was always top of the class. He was an incredible athlete as well, brilliant at basketball and baseball.
He scored more than anyone else in the school's history at basketball and thought about becoming a professional player.
He said it was my fault he couldn't because he'd inherited my hands and they were too small.
He also inherited my love of books and he writes: poetry and a novel that's autobiographical.
Perhaps he'll publish it one day, under a different name.
He sends me all the videos of The X-Files. I get them a week after they've been shown on TV in America.
I've been over to see him in Vancouver, where it's filmed, three times.
It's madness. I don't understand his life at all. People ask for my autograph, even at passport control.
Once, when I was at the fan club's shop in Paris, I had to be rushed out, because there were just too many fans there.
I'm always getting phone calls from people who want to speak to David.
I don't understand these young girls who ring. They want to talk to me just because I'm David's father.
I also get fan letters -- about 10 a month. Some are very nice, others are a bit weird, with pictures. I only send him the nice ones.
David's never been to see me in Paris but I speak to him often on the phone, about six times a month.
It's hard to get hold of him, even though he's got enough phones -- in the car, in his trailer, at his apartments in Los Angeles and Vancouver.
His life's very hard. He makes 24 programmes a year, 10 months a year, and he also wants to make films. He will. He's succeeded in everything he's ever done.
In Vancouver, there are always lots of women around him. It's always been like that since school.
His life's hard because he's cut off from real life. He's on his own a lot, no two days are ever alike. He might start working at five in the morning or not until three in the afternoon, so it's difficult to have a social life, to have a family.
I think he wants to get married and have children, but can't find anyone.
Tea Leoni? Never heard of her. It's difficult to follow his love life. It's always been difficult.
When he says monogamy isn't in his nature, he isn't joking. His brother's the same. In any case, everyone wants him to marry Gillian Anderson.
When David and I speak, I always ask him the same thing: "When are you going to give me a granddaughter?"
He laughs ... and never gives me an answer.