In fact, Aziraphale (Michael Sheen) admits he has a 1965 Doctor Who annual, which prompts the question - who on Earth (or Heaven, or Hell) does he think played the Tenth Doctor?!
Responding to what is, presumably, confirmation of his existence in the Good Omens universe, Tennant told ComicBook.com: "Well, we know that William Hartnell does, because he's on the cover of the annual, isn't he, that you get at the back of the bookshop?"
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He added: "That is a ... But then after that, we could be ... Who knows? Timelines are very complicated things."
Sheen added: "Well, and then also, it turns out Aziraphale is a Doctor Who fan", with Tennant responding: "Of course, he is ... Who isn't?"
Season 2 of Good Omens treated fans to a mountain of Doctor Who references including but not limited to: Crowley correcting a character who called him "Mister", insisting his title is "Doctor", Beelzebub pointing out that the fly in the last episode is "bigger on the inside" and Tennant's Crowley rocking a fez in one scene.
There are plenty of other Easter eggs and references too, including the registration plate on Crowley's car reading the word "Curtain" backwards - a reference to Monty Python.
Previously chatting to The Radio Times Podcast about Easter eggs in season 2, Tennant said: "There are definitely more references - lots that I didn't even get. Every now and then, Michael would tap me on the shoulder and go, 'Have you seen what's in this set? It's a reference to a film!' And I'd be like, 'Ah, I don't know.' I've got weird contact lenses in and I can't really see very much so you're just going to have to help me out.
"There's things in every...some of them are quite explicit, some of them are very subtle, very subtle. But there's a lot of Easter eggs in Good Omens. I suppose things like that are there for an enthused fanbase, aren't they?
"They don't get in the way of enjoying the show as a more casual viewer, they're there as sort of extra content, extra texture for those who wish to do a deep dive, and it may be that this show has some people that do want to do a deep dive. It's all there for you. That has been provided!"
He added: "It's humbling and exciting to be part of a show that means so much, that people get so excited about. It's great to be excited about a show that's fun and full of joy and it's a show about an angel and a demon finding common ground. It's a show about two polar opposites helping each other out, making life easier. If there's a message for this fractious moment..."