LONDON — Stewart Fellner, a Yankees season-ticket holder who traveled from his Long Island home to be part of baseball history, was royally amazed Saturday at London Stadium.

No, it wasn’t the Yankees’ and Red Sox’s 58-minute, 12-run first-inning that left an indelible impression, but rather the company he kept during that marathon of an opening act.

“We had the prince and the duchess sitting behind us for a little while,” Fellner said, referring, naturally, to Prince Harry and his wife Meghan, Duchess of Sussex. “Everyone was turning around and taking pictures. They [the stadium staff] were yelling, ‘Please sit down and enjoy the game!’

“What do you expect? There’s royalty here!”

The royalty lent a most British touch to a ballgame that, aurally, could have been mistaken for Yankee Stadium or Fenway Park. Be they vacationers like Fellner, who had never been to Europe before, or American expatriates, enough patrons knew enough so that Northeast Corridor-specific chants like “Luuuke!” for Yankees first baseman Luke Voit (who departed midway with an injury) or “Mooook!” for Red Sox superstar Mookie Betts thundered prominently.

It felt and looked close to a 50-50 split in terms of rooting interests, and they buckled in for the contest that sped up only a little bit after the opening frame.

“I don’t think it would’ve been 6 to 6 after one [in the States],” Fellner, of Wantagh, said following the completion of the first inning. “But it’ll be a typical Yankee-Red Sox game. It’ll be a long game.”

The novelty mitigated at least some of the standard “Too long!” complaints that litter contests on North American soil. After the Kingdom Choir, a gospel group based in London, performed “The Star-Spangled Banner,” the unit pivoted directly to “God Save The Queen,” the British national anthem, the first time that had ever preceded a baseball game. It generated huge applause, as did Harry and Meghan as they participated in the ceremonial first pitch alongside participants from the Invictus Games.

And after the fourth inning, well more than two hours into the game, the Brits debuted their version of a mascot race, with folks dressed as native icons King Henry VIII, Winston Churchill, Freddie Mercury and the Loch Ness Monster.

The actual Brits in the stands appeared captivated and not at all fazed by the game’s pace.

“It’s amazing,” said Sian Deering of Leicester, whose husband Jamie lived in Fairfield, Conn., for a few years and adopted the Yankees as his team.

“I don’t quite understand all of it just yet, but watching it, the atmosphere is unreal.”

Said Rohan Massey of London: “Somebody said they might find baseball slow. I said I’m a test-match cricket fan. Five days is a short . . . time!”

Asked if he’d make it through all nine innings, Massey pointed to the field and said, “Will they make it through all nine innings?”