This post might have Doctor Who spoilers!
They've announced the actor to play the next Doctor, the 13th Doctor. Jodie Whittaker. She's beautiful. Should be interesting. Bracing for nerd-rage.
I suspect Jodie Whittaker's Doctor is going to turn out to be the grown up Susan Foreman.
The very very first Doctor had three very first companions. Ian Chesterton, Barbara Wright , and Susan Foreman.
Ian and Barbara were Susan's teachers at her school. Susan Forman was the Doctor's granddaughter.
Here's why I think so...
Peter Capaldi's, the 12th Doctor's last scene had him resisting regeneration. He'd sustained much damage fighting off various versions of Cybermen. He got away, TARDIS landed him in some snowy area where he encountered the 1st Doctor.
The 1st Doctor's granddaughter was never clearly defined as such. There were major hints that she was also a Gallifreyan. The lineage was not defined. We don't know who Susan's parents were. We don't know who Susan's parents' parents were! Other than supposedly the Doctor, based on them referring to each other as Grandfather and Granddaughter.
I am going to guess that the upcoming Christmas special will be something like- The 1st Doctor will help the 12th Doctor essentially die. I think since it was kind of established that there are only 12 regenerations to be had, our Doctor is pretty much finished. So maybe when 12 dies, he regenerates into a child. A young female child. And there's the 1st Doctor, ready to take care of her. Perhaps she doesn't know who she was, so without having to explain the complexity of a TimeLord's lifespan and that she is actually him, but much much later in his life; 1st Doctor simply says- your my granddaughter.
Susan adventures with the 1st Doctor for some time. She eventually falls in love with a guy on Earth in 2164.
She did resurface to experience more adventure with the 1st Doctor along side the next four doctors in The Five Doctors.
So the upcoming series with Jodie Whittaker will be about the matured and fully aware and renewed Susan Foreman upholding the Doctor Mantle.
So there you have it. That's my prediction. The 13th Doctor is actually the all grown up Susan Foreman.