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With the pair's return next week on Channel 5 as bickering FBI special agents Fox Mulder and Dana Scully to investigate more episodes of the paranormal, David tells the Radio Times: "We’d spent eight or nine years working together 12 to 14 hours a day. On top of that, we went from complete obscurity to worldwide stardom. Not just America. I think we both went somewhat crazy. It’s such a big change in someone’s life and such a strain on one’s time to make a show like that, so we both went a little nuts. You’d have to, right?
"At times we were nuts with one another, where she [Anderson] was acting crazy or I was acting crazy, or we were both acting crazy. But the thing about being crazy is you don’t know you’re crazy. I look back now and say, ‘Oh, I was a little nuts.’ And I think Gillian would say the same. We both appreciate why the other was crazy. We get it, and forgive.”
'The X Files' made worldwide stars of both David Duchovny and Gillian Anderson
The original series ran for nine years and 202 episodes, making it the longest-running sci-fi show in US TV history. Despite his long tenure in the show, David professes himself far less of a conspiracy theorist in real life.
“People can’t keep secrets. I’ve never known anybody, not one person, to keep a secret. I find it hard to believe that they’re keeping aliens from us because it’s pretty juicy. You come home from work and you go, ‘Honey I’ve got to tell you something, but you’ve got to promise not to tell anybody. They’re here!
"I saw an alien today.’ She’s like, ‘I won’t tell anybody.’ And is then straight on the phone to her mom. That was my problem with JFK. There was no way. If there was a conspiracy to kill the president, somebody talks. Somebody along the way opens their mouth. There are too many people, too many secrets to keep. It’s not human nature. I don’t believe in it.”
Both stars of the show have gone on to enjoy success in other projects, Gillian in a series of BBC adaptations such as 'Bleak House' and 'War and Peace', while David has starred in 'Californication' and, more recently, Charles Manson-inspired crime drama 'Aquarius', a level of fame and prosperity that has surprised the New York-born actor.
“When I was younger, I never looked ahead. No, I just wanted ‘a pot to p*** in’, as my mum would say. I was always afraid that I’d end up in the gutter. That was our fear growing up; not to have any money and to end up homeless.”
He pauses before adding: “I mean, it wasn’t like that was imminent – but my mother was born during the Depression in Scotland and it was different. Just to have a place to live and food to eat was enough, which was a good attitude to have.
“I always wanted to be engaged, creative and imaginative – and to not have to go into an office every day. That was the life that I wanted. I didn’t want to wear a suit and tie, which is the f*****-up thing about having to play Mulder again. When I went in to work, I had to wear a suit and tie.
"It happened with 'Aquarius', too, so I’ve really screwed myself. I’ve got two shows where I have to wear a suit and a tie, which is what I didn’t want to do with my life – but there you go.”
Read the full interview with David Duchovny in this week's Radio Times. The X-Files 9pm Mondays on Channel 5 from 8 February