Even Mr. Alba was surprised by the sartorial choice, saying he assumed the whole thing was a joke when he received an email last March from Jane Gooday, the film’s head costume buyer at Pinewood Studios, outside London.

“I spoke with my personal trainer that morning and he couldn’t believe it,” Mr. Alba said. “He told me not to get my hopes up, that maybe I wouldn’t even get to see my clothes in the film.”

After receiving the look books for Mr. Alba’s spring 2019 and fall 2019 collections, the studio ordered 30 suits, raincoats and trousers from the spring styles, each in three European sizes — 50, 52 and 54. The unlined Sloop suit came in what Mr. Alba called “Desert,” a sandy hue; the duster coat in “Agades,” a moss-green color named after the Niger city Agadez; and the pants in a gray shade called “Alluminio” or aluminum. And the studio paid the bill — though Mr. Alba declined to say just how much it was.

For this was no big-budget product placement deal. Mr. Alba, 59, who started his business in 2006 after stints at the knitwear labels Ballantyne and Malo, has no marketing department or digital communications division (he posts on Instagram himself, where he has about — 14,400 followers). He has six stores in Italy, wholesales to 130 stores worldwide and hosts presentations in his atelier during Milan’s men’s fashion weeks.