Sir Ian's pride at his family roots

The acclaimed actor, who was raised in Wigan, discovers in next week’s show that he has creative family tree, which includes a painter, a singer and an actor.

And as a keen activist for gay rights, he’s also pleased to learn of a great-great-grandfather who campaigned on behalf of his fellow workers.

“They’re not neurotically bound up with their own lives. Whether they’re an actor, singer, social reformer, painter - they’re all outgoing,” he said.

“They’re in the society and are part of it and try and change it. If that is a family trait, I confirm that in my own life.”

Unlike some celebrities’ gruesome or shocking findings on the series, McKellen’s were “all entirely positive” - but he notes that the outcome could have been different.

“This is only one little strand. It’s a lovely strand, but in the whole tapestry of a family, there are hundreds of people to choose them. A friend of mine was asked to do the programme and they did their research and came back and said, ‘We’re sorry, there’s no one of any interest in your family’.’”

He notes that he is the last of the McKellens, but it’s not something he’s particularly bothered by. “I don’t feel anything about it, really. I think I’ve always known I wouldn’t have children, because I’m gay. That wouldn’t have been true today, would it?” says the star, whose older sister, Jean, died in 2003. “I don’t feel I’ve got a responsibility to produce another McKellen.”

In fact, he was “very glad” not to have children.

“Bringing up children is the most dreadfully difficult thing to do, and so few people are good at it. I’m far too selfish. I mean, I know parenthood can change people’s personalities in a good way, but I find it difficult making decisions about my own life. To have to make decisions about someone who’s dependent on you...

“Oof,” he sighs, before adding: “I can see it would be very alluring to look into the eyes of a little boy or girl who looked like oneself, that must be extraordinary, and reassuring in some way. But I don’t look to my legacy, I suppose that’s what makes me different from a lot of people... My contribution has been of another sort.”

Sir Ian’s episode of Who Do You Think You Are? is on BBC One on January 25 at 9pm.