Good Omens producer Rob Wilkins says David Tennant and Michael Sheen were the only two stars who could bring Good Omens to life.
The duo star in the new Amazon Prime Video series, released on Friday, as demon Crowley and angel Aziraphale, respectfully.
The show is based on the book by Terry Pratchett and Neil Gaiman, which tells the story of an angel and a demon who must team up to stop the end of the world.
And clearly, David and Michael were the only choices for show bosses.
During an exclusive chat with Mirror Online at last night's premiere in London's Leicester Square, Rob said: "We've got the best cast and we had the best crew and the best director, and of course, Neil Gaiman adapted it so we've got the best possible person writing the screenplay that we could have hoped for.
"Michael is a huge fan, he read the book, it was his favourite book going through drama school he knew the book inside out, met Neil Gaiman, so was always, always going to be part of the show, whoever and however this happened, Michael was going to be part of it.
"And David, I love David Tennant, Terry Pratchett loved David Tennant, so he's the only Crowley that we could have possibly hoped for.
"During the whole casting process, his name kept coming to the top and we had to get him, and here's the thing, just a few hundred yards away from here he was on stage at the Wyndham Theatre playing Don Juan, and I saw it, I watched it a dozen times, and when he walked onto the stage and talked to the audience, in that moment he was Crowley.
"The magic that they create together, you get these two amazing actors, but together, they're incredible."
Twilight star Michael also chatted about his role alongside the former Doctor Who actor.
He told us: "I think part of what's exciting about me and David is that we never usually act together, I think we're up for a lot of the same parts usually, so there's only room for one David/Michael shaped person in a production.
"So the fact we get to work together in this, and we are quite similar in some ways, I think is a big part of it.
"As the angel, I've got quite a bit of demon in me and as the demon, David has got kind of a good soul, so we kind of mix it up a bit."
The series also stars Jon Hamm, Jack Whitehall and Miranda Richardson.
* Good Omens launches globally on Amazon Prime Video on Friday, May 31
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