A pair of Doctor Who fans received letters from Peter Capaldi on the day of his show departure assuring them he will be "always there, somewhere in time and space".

Brothers David McGilloway, nine, and Tom, 11, couldn't believe their eyes when they opened the personal messages on Christmas Day.

The youngsters have been big fans of the show, and Peter Capaldi in particular, for many years.

And they were sad that he was leaving the popular series after first appearing in a 2013 Christmas special.

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But the pair were over the moon when Capaldi sent them handwritten letters dated back to 23 November 1963 -- the day the first Doctor Who episode was aired.

Writing about his departure from the popular show, Peter Capaldi said "regenerating is not completely good" but insisted that things always "turned out good".

Their dad Brian, 43, said: "Actually, Peter Capaldi sent two letters -- one to David and one to Tom.

"They were delivered by Santa and came in Dalek-illustrated envelopes.

"Peter Capaldi wrote to say that despite the regeneration the Doctor would never be really gone. He said he'd be somewhere in space and time.

"He said, 'Everything ends and it's always sad. But everything begins again and that's always happy'.

"It was such a kind and generous thing to do. It meant so much to them."

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Brian, of Strabane, Northern Ireland, believes Capaldi found out about his sons being fans of the sci-fi show after he met former Doctor Christopher Eccleston.

He explained: "I think it started when I met Christopher Ecclestone around Halloween when he was filming in Belfast.

"I bumped into him and mentioned that my kids loved Doctor Who. I thought they would be so jealous.

"He face-timed the kids and said he'd lost the Tardis in Belfast and that he couldn't find it. He said he needed my help. David was speechless.

"Christopher Ecclestone actually took the time to speak to all of the kids. It was such a kind and generous thing to do.

"Santa must have found out about their love for Doctor Who because they got letters from Peter Capaldi for Christmas.

"It was just a different level of kindness. It was such a kind and magical thing to do on the day of the regeneration. The boys loved it.

"David said it was his best present ever. It was really magical."

Capaldi sent autograph cards addressed to the McGilloway family, wishing them a happy Christmas and personal letters to the two boys.

One of them reads: "Dear David, "I hope you are having 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 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.

"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.

"All the best, "Peter Capaldi "Doctor?"

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Brian, a teacher and dad-of-four, decided to share pictures of David's letter on social media on Wednesday.

It has been liked and shared by fans from around the world.

Capaldi was succeeded by Jodie Whittaker as the Thirteenth Doctor in the 2017 Christmas special "Twice Upon a Time".