The Scottish actor, whose first full episode as the Time Lord is due to air in the U.K. and U.S. on Saturday (23Aug14), was a huge fan of the sci-fi hit when he was growing up.
He amassed an impressive collection of autographs, photos and books, but he ditched the lot when he hit 18 and began drinking in bars.
Capaldi tells British magazine Radar, "I was totally geeky. But when you reach the age of 17 or 18, you move on and discover sex and drugs and rock 'n' roll. I'm ashamed to say I had a kind of bonfire of the vanities. I had a huge collection of Doctor Who books, autographs and pictures, but I threw them all away to go and drink lager and eat curries. That was silly, wasn't it? I wish I'd known that one day the geek would inherit the Earth."