Lance Bass and Michael Turchin Attended the Same Two Halloween Parties Before Meeting: ‘No One Introduced Us’ (Exclusive).Linh

Lance Bass and Michael Turchin‘s love story started on the *NSYNC member’s favorite holiday — even if they didn’t know it at the time.

The pair, who share twins Violet and Alexander, turning 3 on Oct. 13, first ran into each other at a mutual friend’s Halloween party. “We have pictures together, but we didn’t really know each other,” Bass, 45, told PEOPLE before a launch event for his first children’s book, Trick or Treat on Scary Street (out now).

“We have the same best friend circle,” Bass added, which is how he and Turchin, 37, ended up at the same party. “But no one ever introduced us.” At the time, Bass was co-hosting Halloweenie, a charity event. Both were in costume, which Bass says might explain how they didn’t notice each other at the time.

“There’s a big group photo of me and all my best friends and Michael [is] at the end,” Bass explains. “Then, the next day, we’re in different costumes and I have another picture with him, with another friend of mine, just the three of us.”

Bass is a big Halloween fan, often dreaming up multiple costumes for himself — and now his husband and kids — to wear throughout the season. He told PEOPLE he doesn’t remember exactly what he was wearing the first time he and Turchin met. “Usually I just go for the scary, gory stuff,” he says. “But I remember the second one, because it was embarrassing.”

The singer wasn’t planning on going out that night, but he was invited to a friend’s hotel rooftop party at the last minute. “But I didn’t have a costume. And, you know, I take it very seriously,” he explains. “So I went and got my flight suit from my Russian Cosmonaut training. So I went as Lance Bass, in my actual flight suit, which is so cheesy.”

For six months in 2002, Bass trained in Star City, Russia, to become a certified cosmonaut. He later became certified by both the Russian Space Program and by NASA for the Soyuz TMA-1 spacecraft mission, although his financial backing fell through before the 2002 mission took off so his suit never made it into orbit.

But for a last-minute Halloween costume “it worked,” he says, adding that he put “some little aviators on, like Top Gun” to really sell the look. “And it fit perfectly.”

It wasn’t until two months after that second party, when Bass and Turchin were introduced at a friend’s birthday party in Palm Springs, that they formally met.

“That was when he was out of makeup,” Bass says, with a laugh. “And I’m like, ‘Oh, who is this guy?’ “

Turchin, an actor and artist who’s originally from Miami, later sent Bass a Facebook poke. “I think it might have been the first Facebook poke I ever got,” Bass says, with a laugh. “And I’m like, oh, that was that was the cute Michael guy … I didn’t think he liked me, so in my head I’m like, okay, I need to become best friends with this guy.”

“So I get over the attraction,” Bass explains. “We spent every day together as best friends for two months before we knew we liked each other. And then he leaned in for a kiss two months later … and yeah, we haven’t spent really many days apart since.”