Ralph Fiennes was hanging out with a Catholic cardinal.
The “English Patient” actor was preparing for his next role, as Thomas Cardinal Lawrence in the pope movie “Conclave,” in theaters Friday, and wanted to spend time with the real deal.
Head-first Fiennes went a bit further than that.
“I get a text from Ralph, who had met a cardinal, and the cardinal had invited him to his chambers,” Oscar-winning director Edward Berger told The Post.
“On the bed in his chamber was laid out the cardinal robe,” Berger continued, “and then Ralph sent me a [photo] of him … in those robes, in the real robes, with a beaming smile … so proud.”
There was a problem, however, because Berger, who directed Best International Feature winner “All Quiet on the Western Front,” was going in a different direction with the official’s outfits.
“The costume designer and I knew that we don’t love the way the present-day cardinal robes look,” he said. “The red is a little bit orangey and the fabric is not as luscious as you might think.”
But, as actors often do, Fiennes, 61, had instantly clicked with the garment.
“I needed to call him and say, ‘It looks great, but that’s not what it is going to look like,’” Berger recalled. “He said, ‘Look, that’s the real thing.’ And so it took a little bit to convince him to put on this one.”
Clothes weren’t the half of it.
Berger and production designer Suzie Davies (“Saltburn”) went to extraordinary measures to re-create, embellish and occasionally invent the mysterious world of Vatican City and the papal conclave, the secretive meeting of cardinals who pick a new pope.
“They won’t tell you what happens behind closed doors in the conclave,” the director said of the tradition-bound church. “And there are certain things you have to take license with.”
And as “Conclave,” which also stars Stanley Tucci, John Lithgow and Isabella Rossellini, is a scandal-packed thriller based on Robert Harris’ controversial 2016 novel, the Vatic an did not shout “Come on in!” to Berger and his cameras.
“There’s a white line on St. Peter’s Square,” Berger said. “And that white line means no commercial photography allowed beyond this point. And so, [we had] to re-create the feeling of the Vatican — the cohesiveness of the Vatican — by picking and choosing many locations in and around Rome.”
Even the best location scout can’t find a look-alike Sistine Chapel. That meant Davies and her team had to build one from scratch.
“We managed to get into the Sistine Chapel without any other tourists,” Davies said of a special research trip. “It was with a lot of security.”
But, she added, “I was able to feel the essence and see it as bare as possible to take that essence and that amazing artwork and the curious nature of it.”
Davies and a crew of Italian artisans then re-created the chapel at Rome’s Cinecittà studios, where “Cleopatra,” “Ben-Hur” and “Roman Holiday” were also filmed.
Michelangelo is a tough act to follow, though, so technology was used to replicate the world-famous ceiling.
“It’s the Sistine Chapel for a reason, you know?” Berger said. “It only exists once in the world. There’s one guy who made it.”
So, the painted ceiling, including “The Creation of Adam,” is a smooth CGI extension.
Davies and Berger had to get more creative with the off-limits Vatican residences, which stand near St. Peter’s Basilica.
“Our tour guide did point across one of the courtyards in the Vatican City and said, ‘That’s the Casa Santa Marta,’” Davies said. “I think we both thought, ‘Well, that’s a pretty dull looking building.’”
They couldn’t get inside, but its outer averageness proved inspirational. To juxtapose the apartments with the grand Sistine Chapel on-screen, Berger chose an off-kilter role model: prison.
“Because they are sequestered, they’re locked away,” he said. “So what’s the equivalent visually when you’re locked away? How do you make that feel? Like a jail.”
We’ll see how the 234 international cardinals feel about being depicted as sleeping behind bars — they’re planning to buy tickets to “Conclave.”
“We spoke to cardinals beforehand who gave us advice and told us things and invited us into that world,” Berger said. “And they did say, ‘We’re going to be watching this movie.’ And it was kind of [with] a smirk.”
The director added of his juicy film that depicts explosive, ugly political battles inside the Catholic Church: “I think they’re going to have fun watching. I think they’re kind of looking forward to it.”