New/old showrunner, Russell T Davies, has teased that there is a specific reason behind David Tennant and Catherine Tate returning to Doctor Who; it wasn’t merely a whim. You might’ve gathered that already though.

In the latest issue of Doctor Who Magazine, Davies writes:

“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.”

If anyone is thinking that this is a sort of acrostic, then they’ll have realised that this hidden truth is: “AOMTONOBTST.” From this, we can infer that… maybe one’s an Auton? Or, ahem, a nob? Or maybe it’s an acronym! Or it could be none of the above and our brains have started dribbling out of our ears.

So what can we gather from this?

Realistically, it’s looking less likely that it’s the first option, i.e. that the 60th anniversary special takes place between episodes of Series 4. For one, the Doctor looks decidedly different, i.e. he’s wearing a (slightly) different outfit. Also, it appears that Yasmin Finney is playing Rose, seemingly Donna’s daughter. That’s speculation, but very likely.

The illusion could hint at Neil Patrick Harris as the Toymaker — who, in the character’s previous story, made the Doctor invisible.

Personally, my money’s on a regeneration gone wrong, with the Doctor reliving a previous face… although why and how Donna’s there too is a mystery.

I guess we’ll see in the upcoming 60th anniversary celebrations. But what are your theories, dear DWC readers?