When Tom Ni, a 29-year-old California native, was prepping for his Queens wedding last September, the marketing exec figured he’d rent a tux and be done. Little did he know he’d be in for a day of beauty treatments at his bride’s urging.

“I know next to nothing about makeup,” says Ni sheepishly. “I was nervous.”

He wound up spending $330 to beautify on the big day — $200 for a top-of-the-line anti-aging sheet mask, as well as $130 for additional skin treatments (including a firming placenta-based eye patch) and barely there makeup.

Often at the behest of their soon-to-be wives, men are now partaking in typically female rituals before a trip down the altar. They, too, are shelling out big bucks — it’s not uncommon for a bill to spill into the four figures when groomsmen join in. Treatments might include mani-pedis, airbrushing and, yes, even makeup touch-ups so that even the guys look flawless come photo time.

“They were telling me what they were doing, but the explanation was entirely lost on me — something about foundation,” says the cosmetically clueless Ni.

‘It’s a nice thing for them to do to feel special, too.’

But all the primping was worth it once his bride, Lily, set eyes on him.

“My wife gave me a once-over with approval — we both laughed,” he says.

Makeup artist T. Cooper, co-partner of NYC’s Metro Look beauty company, who worked with Ni, says groom-focused beauty has been a growing part of her business over the last two years.

“It’s a nice thing for them to do to feel special, too,” says Cooper, who last summer charged a groom and his party of five guys $1,500 for a day of facials, mani-pedis, tattoo coverage with concealer, foundation and powder on necks and faces out in the Hamptons.

Not all her male clients are groomsmen.

Cooper recently worked a wedding where the bride’s acting maid of honor — Jeffrey Ware, whom she describes as a “masculine” dude — had his makeup done right alongside his bestie.

After application, Cooper recalls, Ware admired himself in the mirror and gushed, “I’m not used to seeing my skin look this flawless! I don’t want to touch my face and ruin it.”

Fellow makeup artists say the surge in male grooming is a direct byproduct of today’s selfie culture.

“Social media drives a lot of it,” says New Jersey-based Samantha Agostino, who notes that the entire wedding party usually documents the process in real time. “Even the brides and grooms take selfies of themselves — during the first look and before they walk down the aisle,” she says.

Agostino recalls a wedding party last year where the guys didn’t want to be left out in the cold. “They said, ‘Can you make us look fabulous too?’ ” So she worked her magic with powder until the three groomsmen were photo-ready.

But if metrosexual men are embracing this new era of liberation, they aren’t leaning into their femininity too much. One shy groom anxiously asked Agostino, “It’s not going to look like I’m wearing makeup, right?”

Others are all too happy to go with the flow, especially when the weather wreaks havoc on their skin.

For his Montauk Yacht Club wedding in October, unseasonable heat caused Tyson Evans to enlist the Agostino for a shine-free look. His bride splurged on a makeup package that included herself, her seven bridesmaids and the groom.

“I definitely wanted to make sure I looked as good as I could so our photos would look amazing,” says the 39-year old, who works in education. He got the works: pedicure, lip treatment without shine, concealer on the lips to reduce redness, foundation and Make Up For Ever HD translucent oil-free powder.

Evans’ pals were supportive. “They’re all guys’ guys. Everybody was getting fancy and were like, ‘Let me throw on a little bit of blush or toner or whatever,’ ” he says.

“It made me feel like I deserve this day,” Evans adds. “I deserve to look good and feel really confident going into that ceremony.”

His bride, Kristen Kanopka, a 32-year-old music publicist, loved his new look. “I just got a kick out of him getting touched up,” she says. “He’s a Texas boy who’s not used to that.”

After all, there’s no shame in the makeup game, say grooms.

“If it’s really threatening to your masculinity, you might want to think about that,” says Ni. “There’s a certain amount of pageantry to it — why not?”

Still, he says, “I haven’t worn makeup since.”