Plus: How will their son play into the new miniseries?

By Michele Corriston
Updated January 24, 2016 06:25 PM

The truth about Dana Scully and Fox Mulder’s relationship is out there – but viewers will have to wait until the X-Files miniseries premieres Sunday night to find out what’s driven a wedge between the FBI’s spooky duo.

It took seven seasons and two movies for Gillian Anderson and David Duchovny‘s characters to move beyond a platonic partnership. When the new show picks up, Scully and Mulder aren’t together anymore, though their chemistry crackles as hot as ever.

“In the first episode, they’re no longer a couple. They’re living apart. They have not had that much contact with each other,” Anderson, 47, tells PEOPLE. “Obviously there is a child between them, and so they’re always going to be connected in that way. But it feels a little estranged at the very beginning, which is kind of how it always was. It was this tension between the two of them which is part of what worked with the series and which drove the series, so it’s actually an interesting way I think for us to begin again.”

That child, of course, is William, their son born in season 8 who possessed supernatural abilities. Ultimately, the couple gave him up for adoption for his own protection.

Snippets from the miniseries show Scully and Mulder discussing the pain of losing him, but could William, now a teenager, show up on screen?

“Sort of,” Anderson says simply. “Sort of.”

In an interview with Entertainment Weekly, Duchovny, 55, said he’d be “open” to more X-Files after these six episodes wrap up: “Certainly, we didn t bring it back with the idea of ending it.

It turns out Anderson – who’s currently shooting season 3 of the BBC and Netflix’s addictive serial killer drama The Fall – is also a believer.

“It depends on many different factors. Scheduling is a big thing,” she says. “I m open to the discussion.”

The X-Files airs Sunday at 10 p.m. ET on Fox.