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Taron Egerton, Channing Tatum and Colin Firth star in Matthew Vaughan’s spy sequel ‘Kingsman: The Golden Circle.’
20th Century Fox

The running mantra of Kingsman: The Secret Service was “Manners maketh man,” though for the spy movie’s successor, it’s more like “Sequels driveth the director mad.”

“Making this film has been the hardest endeavor I’ve ever done in my life,” says British filmmaker Matthew Vaughn, who’s taking a break from finishing Kingsman: The Golden Circle (in theaters Sept. 22) to promote the film to ravenous fans Thursday at San Diego Comic-Con.

“I genuinely had no idea how difficult it was. But I’m happy with the end result. You need a bit of time for the bruises to go before you start remembering the good stuff.”

After saving the world from the nefarious businessman Valentine (Samuel L. Jackson) in 2014’s original Kingsman, newly minted superspy Eggsy Unwin (Taron Egerton) and what’s left of their covert British organization — including Merlin (Mark Strong) and Roxy (Sophie Cookson) — have to scramble in the sequel when their headquarters is blown up.

They come to the USA and join up with their American counterparts in Statesman, a bunch of wild spirits including Southern secret agent Tequila (Channing Tatum), whip-cracking Whiskey (Pedro Pascal), tech guru Ginger Ale (Halle Berry) and their leader Champ (Jeff Bridges).

The resulting team-up is “a healthy rivalry with cultural clashes,” Vaughn says. “There’s a great line that Churchill said about America: The only thing we really have in common between England and America is the language, and even that’s debatable.”

While the first Kingsman was “very much a…