David Tennant was worried his son Ty would be ''rubbish'' at acting.

The 49-year-old actor's 18-year-old adopted son - who is the biological son of David's wife Georgia Tennant, who gave birth to Ty before she met David - is following in his parents' footsteps as an aspiring actor, having appeared in last year's 'Tolkien', and TV series 'War of the Worlds'.

And now, David has confessed that he and Georgia - who also have Olive, nine, Wilf, seven, Doris, five, and Birdie, 11 months, together - were concerned when Ty first started acting, as they didn't know what to do in the unlikely event that he wasn't cut out for Hollywood.

David said: ''Acting is a crapshoot anyway, and Georgia and I had this fear when he went into it of, what if we see him in something and he's rubbish? Will we be able to tell him? But as it turns out, he's incredibly talented. Which was a great relief to realise!''

The 'Good Omens' star keeps his family life out of the public eye, and whilst he says being a dad is ''one of the most extraordinary things'' he's ever experienced, he doesn't like to open up about his brood.

He added: ''Our kids are lovely, and I think that being a dad is one of the most extraordinary and life-affirming things that can ever happen to you, as well as being something you have to keep working at if you're going to be any good at it.

''But the kids don't ask to be photographed when we're walking down the street, and we've decided that if we don't talk much about them in public, then we can maintain a bit of moral high ground to be able to say to photographers, 'Look, we don't talk about them, so you don't need to take their picture'.''

David wants to allow his children to ''live as normal a life'' as possible, and said that whilst he knows fame comes with a price, he thinks it's possible to ''preserve a bit of private life, too''.

Speaking to Candis magazine, he added: ''We don't want to be silly about it but we just want to try to live as normal a life as possible outside of work. I am hugely privileged to be a part of the world I am part of, and I knew what I was getting into when I entered it. But I think it is possible to preserve a bit of a private life, too.''