FBI special agents Fox Mulder (David) and Dana Scully (Gillian) are back for another six-episode series, nearly 23 years after the sci-fi series first aired.
The screenwriter said: “It was like the old days, and we all hit the ground running.
“People want to know what that first day was like, getting back together – you would imagine that it would be a lot of smiles and back-slapping.
“I’m telling you, we had so much work to do on that first day, that no one had a chance to even, I think, recognise that personal, ‘We’re back together after eight years apart’.”
The X-Files originally ran for nine seasons until it ended in 2002, and led to two feature films – with the last one in 2008.
Since the end of The X-Files, Gillian has gone on to star in The Fall, while David has been in Californication and Aquarius.
But the paranormal drama has been revived with a special “event series”, due to air on RTÉ2 from this week.
Chris said he had kept Mulder and Scully in mind over the years.
He explained: “I think about it all the time. I’ve been doing this now for nearly 25 years, so these characters are in my blood.
“When I pick up the newspaper, I almost always see something that could work as an X-Files episode.”
The mini-series opens with Mulder and Scully no longer in a relationship.
“I’m honest to where I believe they would be in their lives, based on all that we have established in the mythology,” Chris said.
“And in the second movie, where they were together, I thought naturally they would arrive at a bump in the road, based on what their characters are, and their individual pursuits.”
The return of The X-Files has stirred up hope among fans of the show, who are keen for more than a six-episode comeback.
Chris said: “It’s funny, it’s not, like, not enough that you’re coming back. It’s like, are you coming back for even more?
“I think it’s a natural thing, it’s like – are we going to go on a first date, are we going to go on a second date?”
He added: “Fox did ask me a question about more, but it was sort of like an off-the-cuff thing, and they were wondering if there were going to be more, when that could be.
“I had no good answer for them because I don’t know. But I think that everyone is waiting to see how we do in the ratings.”
The “abbreviated season” will end with a cliffhanger.
Chris explained: “We don’t want to tie up all the loose ends, it might suggest that we’re done with the show.
“But I’ll leave it as a question: are we done, are we not?”
The reboot of The X Files is shown on RTÉ2 on Tuesdays, just two days after it airs in the US.