Returning Doctor Who executive producer Russell T Davies has teased the storyline that will bring David Tennant and Catherine Tate back to the show.
Earlier this year it was confirmed that the pair would be back as The Doctor and Donna Noble for next year's 60th anniversary special - and in recent weeks, they have been spotted filming scenes together in London.
Tennant's Doctor regenerated in 2010, while Donna's mind was wiped on the proviso that she would die if she ever remembered her time with The Doctor, leading to much speculation about how they could possibly both come back.
Writing in this month's Doctor Who magazine, Davies said: "A mysteriously forgotten excursion for the TARDIS in between Planet of the Ood and Sontaran Stratagem? Or maybe a multiverse thing, they're all the rage these days. Maybe this is the Doctor and Donna from Universe 557, all set to collide with our own.
"Then again, maybe, just maybe, this return is so impossible that it's actually an intricate illusion created by an old enemy of the Doctor's. Or maybe an old enemy of Donna's. Nerys!
"Of course, I wouldn't give that away in the pages of DWM, would I? But then again. This magazine is the first place I ever revealed the name of Billie Piper's Rose (in issue 340). So read carefully. There are truths in here."
The special is expected to air in November 2023, around 60 years after the first ever episode was broadcast on November 23, 1963.