In Doctor Who Magazine 579, Doctor Who showrunner Russell T Davies teased shared several possible scenarios for why the Fourteenth Doctor resembles the Tenth Doctor (David Tennant):

“A mysteriously forgotten excursion for the TARDIS in between Planet of the Ood and Sontaran Strategem? 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.”

Donna Noble (Catherine Tate) Married Shaun Temple (Karl Collins) in 2010 and they have a teenaged daughter named Rose (Yasmin Finney). There is nothing which would indicate Donna’s life hasn’t progressed naturally from the known universe or is part of a forgotten 2008 excursion.

In video of the making of the Thirteen-to-Fourteen regeneration, Davies clarified that the Fourteenth Doctor is not an illusion, a joke or the planned trick of a foe. At first glance, there don’t appear to be any truths in Davies’ original tease.

“He is the Fourteenth Doctor because he’s not a trick Doctor. He’s not a pretend Doctor. He’s not a jape. He’s not a plan by the Trickster or anything. He is genuinely the Fourteenth Doctor. There’s something subtler going on that does get revealed.”

So what is the subtle thing? There are a few clues. The Doctor must work out why he got his old face back and why he runs into Donna again after all these years.

“Now, I’ve got this friend, called Donna Noble,” the Fourteenth Doctor muses to Shirley Ann Bingham. “I had to wipe her memory to save her life. If she remembers me, she will die. So what happens next? A spaceship crashes right in front of her. It’s like she’s drawing us in. I don’t believe in destiny but, if destiny exists, then it is heading for Donna Noble.”

Donna absorbed the Doctor’s knowledge abilities in a phenomenon known as a Metacrisis. This crisis would have killed her had the Doctor not wiped her memory. But what if Donna’s memories are the key to save Earth from an alien threat? Rose may also have part to play in the mystery. Could she have inherited Metacrisis capabilities from her mother?

Doctor Who will return in November 2023 with three 60th anniversary specials starring David Tennant as the Fourteenth Doctor and Catherine Tate as companion Donna Noble titled The Star Beast, Wild Blue Yonder and The Giggle.

Ncuti Gatwa will star in his first full Doctor Who episode as the Fifteenth Doctor in the Doctor Who Christmas special alongside Millie Gibson as companion Ruby Sunday in December 2023.

A new 8-episode Doctor Who series starring Ncuti Gatwa as the Doctor and Millie Gibson as Ruby will debut in Spring of 2024.