Robert Gsellman of the Mets pitches in the first inning...

Robert Gsellman of the Mets pitches in the first inning against the Milwaukee Brewers at Citi Field on Monday, May 29, 2017. Credit: Jim McIsaac

Robert Gsellman was adorned in crown and robe — the regal trappings of the player most responsible for the Mets winning the game — when he found out.

What was his reaction, someone asked him, when he learned he likely will be shipped to the bullpen soon?

He barely hesitated, the robe did not slip and the crown did not budge from his nest of long brown hair. “No reaction. I do whatever for the team,” he said.

He was being 100 percent truthful, because that was the first he heard about it.

Hours after general manager Sandy Alderson said Gsellman likely will move to the bullpen after Seth Lugo and Steven Matz return from their elbow injuries, the righthander put together a veritable gem of a start, mostly saved a ravaged bullpen and added two RBIs in the Mets’ 4-2 win over the Brewers at Citi Field.

“That’s the guy we saw last year,” manager Terry Collins said. “That’s the guy we know he can be. He threw the ball very well. He fed off his last outing and I think his confidence is back a little bit.”

Not that this is going to change the Mets’ mind, but while Gsellman said he prefers to start because “starting is a little more fun,” the California cool vibe runs deep with the 23-year-old. The bullpen is just fine with him as long as he’s pitching the way he wants to pitch. “It’s still pitching,” he said, “and I enjoy pitching so much that I don’t care.”

He enjoyed it plenty during Monday’s Memorial Day matinee. He allowed two runs, three hits and two walks with five strikeouts in seven innings. His sinker was especially sharp and, after the second inning, only one playable ball was hit in the air.

When the Mets, clinging to a 3-2 lead, loaded the bases with two outs in the sixth, Collins trotted out Gsellman, even though he still had Neil Walker — hitting .400 with runners in scoring position — on the bench. His full-count walk netted the Mets the insurance run they so desperately needed.

“Every time you have a great outing, confidence goes up,” said Gsellman (3-3, 5.75 ERA), who’s strung together two strong starts. He was effective “just keeping it down, attacking the zone and keeping it on the plate, get ground balls and that’s what I like. Easy outs,” he said. “I’ve been working hard with Dan [Warthen, the pitching coach] with [the sinker] and I’m glad it’s paying off.”

The Brewers scored an unearned run in the fifth inning against Gsellman on Asdrubal Cabrera’s throwing error, a single, a sacrifice and a groundout.

That wasn’t good enough to compensate for Brewers pitcher Matt Garza’s unraveling in the bottom of the inning. Cabrera and Wilmer Flores had back-to-back singles, Rene Rivera’s double to the leftfield corner drove in the first run and Gsellman’s sacrifice fly produced a second. Michael Conforto added an RBI double to right to make it 3-1.

Flores was 3-for-4 and has nine multi-hit games in 13 starts this year.

“When you’re not playing every day, you want to do something,” he said. “I try not to think about that. I go up there and still have my confidence [like] I’m playing every day.”

The Brewers cut it to 3-2 in the sixth when Domingo Santana launched Gsellman’s 0-and-2 curveball off his shoetops over the leftfield fence.

Paul Sewald was perfect in one inning of relief and Addison Reed worked around back-to-back singles to lead off the ninth for his seventh save.

We may not see very much of Robert Gsellman, Mets Starter, in the near future, but Collins seemed confident that Gsellman’s fortunes don’t lie with a setup role in the bullpen.

“In the big scheme of things . . . when you look down the road, you’re never going to know where Zack [Wheeler] is going to be innings-wise,” he said. “And you look way down the road, this kid is going to be a quality starter in this league, in my opinion.”