RHONY Alum Jill Zarin's Daughter Ally Shapiro Is Engaged to Jordan Bilfeld! All the Photos

Though Ally Shapiro's engagement to Jordan Bilfeld was a total surprise — her mom, Real Housewives of New York City alum Jill Zarin, knew a proposal was in the works, she just didn't know when it was going to happen.

"Seven months, I didn't say a word," Zarin tells PEOPLE in an exclusive interview.

Bilfeld has asked Zarin for permission months earlier, but as time continued to pass she wondered if he had cold feet. During a recent family cruise through Europe, she confided in her daughter that she was worried it might never happen.

"It's the second to last night of the cruise [and] we were having this heart-to-heart discussion," Shapiro tells PEOPLE. "For the first time ever, my mom says, 'You know, Jordan's been telling everyone he's going to propose to you this summer and he hasn't yet.' I'm like, 'Why do you say that?' And she goes, 'Well, he asked me seven months ago, and he still hasn't asked you yet.' "

Little did Zarin know Bilfeld was planning on proposing to Shapiro the very next day.

"I decided not to tell her exactly when I was doing it," says Bilfeld. "But I knew we were going on this nice cruise to Europe, and it started in Rome, and it went to Corsica and Portofino and Cannes and Mallorca and Barcelona and I thought, 'Well, that would be a great place to do it at the end of the summer.' But I didn't tell them."

After secretly organizing for months, "I had this whole thing planned," Bilfeld tells PEOPLE. "Jill let it slip the night before."

"The whole night's a mess, and the next morning I have the ring in my pocket, and then [Jill's] boyfriend, Gary, he starts talking to me," Bilfeld says. "He's like, 'You know, it's the end of the summer, you haven't done it yet. September's coming around. When do you think you're going to do it? It could go either way. They all thought nothing was happening on the trip."

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The next day, following a beachside lunch in Mallorca, Bilfeld revealed his surprise, proposing to Shapiro after asking her to take a stroll to a nearby pool overlooking the ocean.

"He starts talking, and I'm freaking out. I'm blacked out. I'm wearing a cover up, no makeup, bathing suit," Shapiro says. "We're just having lunch, and then he was like, 'Will you marry me?' "

The surprise, she adds, was "beautiful."

And the special moment was caught on film, as Bilfeld had organized photographer he found via social media who was snapping photos surreptitiously.

After proposing with a 5.25 carat platinum and diamond ring from jeweler Joey Alibayof of Alexa Trading, Bilfeld pointed to the cameraman.

"And a whole crowd starts applauding," he laughs.

Shortly after, Zarin and her boyfriend Gary — who had been busy paying the lunch check — walked down, too, without having any idea of what had just transpired.

Zarin asked, "Oh, look, why is everyone applauding?" then she realized what had happened. "I get up, and I look over the balcony, and I'm like, 'Oh, my god. That's my daughter.' And I flip out, of course, we run down," adds Jill.

When they got back on the ship, Bilfeld had the couple's room decorated with balloons and champagne — and the celebration continued back home in the Hamptons, where he had secretly planned an engagement party on the beach over Labor Day weekend.

"I was so impressed because not only did they get engaged so beautifully, Jordan, when they got back on the ship, had the whole room decorated with all kinds of balloons and champagne," says Zarin. "What I was even more impressed with is that he had already planned an engagement party in the Hamptons on the beach with his parents and his brother and sister coming into town, because his parents lived in Florida, that they were flying in the Sunday of Labor Day weekend, and he had it all done."

The couple tells PEOPLE they are in the early stages of wedding planning, and hope to host a celebration for some 300 friends and family. For now, they're enjoying engagement bliss as she shared her reaction to getting engaged in photos on Instagram featuring her new diamond sparkler.