The outgoing Doctor sent a letter to nine-year-old David McGilloway, which he opened up on Christmas Day.
David's dad, Brian, shared the note on Twitter - explaining that Glaswegian Peter Capaldi was his son's favourite Doctor, and he was worried about the changes that were coming on the Christmas special.
His post has since been liked more than 4,000 times with more than 1,500 'retweets'.
Peter Capaldi's time as the twelfth Doctor came to an emotional end on December 25, handing over to the first female actor to take on the role - Jodie Whittaker.
The letter, dated November 23, 1963 (the date of the show's very first episode), reassures young David that the Doctor "never really goes".
He wrote: "Dear David, I hope you are enjoying a very merry Xmas. Xmas is always good fun. Well not always. Not every single second. Regenerating is not completely good fun. And it usually happens about Xmas-time.
"But you know what? Even though it can be a little bit icky (like REALLY bad flu) it has always, always turned out good for Doctor Who."
The letter continues: "The new Doctor becomes your favourite Doctor and the one that goes ... well he never really goes, he is always there, somewhere in time and space and if you think about him hard enough you'll see him and he'll see you.
"It's like the doctor says, everything ends and it's always sad. But everything begins again and that's always happy. Be happy.
"So have a brilliant Xmas, a happy New Year and a wonderful life - I'm sure you will."
Via: The Daily Record
