'Doctor Who' star Peter Capaldi sends beautiful letter to kid worried about regeneration

It's always sad when your favourite Doctor leaves the show to make way for a newly-regenerated Time Lord. But they're never really gone, are they? And it always works out best for Dr. Who.

That's the advice that one distraught young Peter Capaldi fan received from the man himself, handwritten with a custom picture of a Dalek.

Dad Brian McGilloway tweeted pictures of the letter Capaldi sent to his 9-year-old son David, who was worried about his favourite Doctor leaving the show. Dr. Who regenerated this Christmas and will now be played by Jodie Whittaker, the show's first woman Doctor.

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"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 Dr. Who. The new Doctor always becomes your favourite 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," Capaldi writes.

David received the letter via Santa, and he was "speechless and so surprised," according to the BBC.

It's not the first encounter with a former Doctor for dad Brian -- he met Christopher Eccleston when he was in Belfast.

The sweet photos shared by teacher and author McGilloway prompted others to share their letters and encounters with Capaldi.

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As Capaldi said in his final speech as the Doctor, "Always try, to be nice and never fail to be kind."