She's also starred in high-profile TV series such as Great Expectations and The Fall, and can currently be seen as society schemer Anna Pavlovna in the BBC's War And Peace.
But both agree that, even after all these years, a return to The X-Files set felt like coming home.'In many ways The X-Files never left me - much as I would have wanted it to,' says David, 55.
But it wasn't just the spooky plots that had viewers hooked.
She's also been candid about having lesbian relationships in the past, and although single now she suggested last year she was not closed to the idea of entering another one, saying, 'To me a relationship is about loving another human being; their gender is irrelevant.'Since The X-Files ended, both she and David have found success with other projects.We understand that we're the only two people who have had this experience together.I think we'd have been better served if we'd realised that earlier on in our lives…but right now it's really good.'I think the coolest things we do are the quintessentially Mulder and Scully moments, the scenes in Mulder's office when we're discussing cases where he's throwing pencils or eating sunflower seeds - they're a lot of fun.'But the whole thing was a little more challenging than I'd expected,' she admits.'Mostly because I've been working hard since the series ended to play women without a trace of Scully in them, and on the whole they've been far more serious than Scully was.