On Monday, Doctor Who fans around the globe said their goodbyes to the Twelfth Doctor, played by 59-year-old Scottish actor Peter Capaldi, in the highly-anticipated Christmas special that aired on BBC One and BBC America. As the longest-running sci-fi show on TV, the character of the Doctor has been played by many different actors. What has made Peter Capaldi such a compelling actor for the role is that he himself has been a Doctor Who fan since childhood. It’s also what makes Capaldi’s letter to a 9-year-old Doctor Who fan that much cooler.

On Twitter, Brian McGilloway posted a photo of the handwritten letter he received from Capaldi, addressed to his 9-year-old son David. McGilloway revealed that his son was very nervous about the Doctor’s regeneration scene in the Doctor Who Christmas special. (A quick primer on lore: The Doctor is a time lord who can travel through all of space and time and is immortal. He doesn’t die, but rather, he “regenerates,” meaning that a new actor assumes the role.) 

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Capaldi had some amazingly reassuring words for his young, worried fan. “Regenerating is not completely good fun,” Capaldi wrote. “Even though it can be a little bit icky (like really bad flu) it has always, always turned out good for Dr. Who.” Here’s the whole letter below—and get your tissues ready.

Perhaps the most moving passage of Capaldi’s letter is the reassurance that the Doctor is always out there, no matter what. (Much like the many, many tributes to Carrie Fisher pouring in on Twitter on the first anniversary of her passing on Wednesday.)

“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.”

I’m not crying, you are! 😭 😭 😭

With British actress Jodie Whittaker joining the show as the thirteenth Doctor—a role held by men for the last 54 years—the show is still as popular as ever, with fans excited to see what a female actress can bring to the almost-sacrosanct role. And if Capaldi’s letter to his young fan is any indication, we have nothing to worry about just because the Doctor has a new face.

Did you watch the Doctor Who Christmas special? Share your reactions in the comments!

—Keiko Zoll