Don't own Harry Potter or doctor who

_

Prolong

When the doctor got his memory and powers back he left. Although he did not notice, that he left the watch behind with some of his regeneration powers still with in it. The family he was with decided to keep it and return it. When they next saw him.

So time went on and the doctor forgot about The watch, but the family he created did not. The watch was passed down, Till the watch was in the hands of little Lilly Evens. while the reason for her family to keep the watch was forgotten. They all knew the watch was special.

So the watch as you know contains part of the doctor's regeneration powers but also some of his memory. so if one of Lilly's family members, had opened the watch they would have been able to activate a dormant gene the all had. But since no one did Lilly gave the watch to her son before she died. To Lilly it was the last piece of her father so she brought it with her to Hogwarts. To keep it safe, she had put notice me not charms on the watch.

Now because of this Harry had the watch with him. The night his parents died.

11 years later...

When Harry and the dursleys were hiding from the wizards, and before Hagrid came to get him. Harry Potter opened the watch

Two Galaxy's away...

The Doctor was standing at the Tardis console

when he felt the birth of a new time lord.

And one with energy similar to his own, This then caused the Tardis to go Three years after the birth.