Christmas came early this year for 11 lucky superfans of Cassandra Clare's bestselling "Shadowhunters Chronicles" franchise when ABC Family’s Pop Up Santa surprised them with a magical fan experience in New York City. There were plenty of happy-tears, angelic rune cupcakes and selfies with Matthew Daddario to go around.

More than 100 impassioned fans from around the country submitted videos detailing what "Shadowhunters" meant to them, and while Clare watched many of the submissions, she decidedly couldn't help choose the winners because they all made her cry.

"I had such a hard time watching them," Clare told MTV News before the big surprise. "I couldn't stop crying while I was watching them. I kept weeping. I literally couldn't pick somebody. They were all so wonderful. I couldn't do it. It was too hard."

When it came time to plan her Pop Up Santa surprise, however, Clare was all in. The fans thought they were coming to NYC to hang out with Clare for an intimate meet-and-greet, but they had no idea what she had planned for them. Each lucky fan received a copy of her hotly anticipated new novel, "Lady Midnight," before it’s available for purchase on March 8 -- but the night's biggest surprises were hiding just around the corner.

"I love meeting people who love the books and love the characters as much as I do," Clare said. "For them, it's amazing to see the characters brought to life -- and for me, too -- so that's something that we can be excited about together. It's fun. It gives me an opportunity to be a fan with my readers. We can talk about things together."

"I have this sense of being in the fandom as well as being the creator of the source material that this fandom is based on, so a lot of times I feel like we're fanning together over the same stuff," she added. "I always think, 'As a fan myself, what would I be excited about? What would I really want? And are we giving that stuff to them?'"

So in order to pull off the night's biggest surprise, Clare needed a little help from her friends, the (super attractive) cast of Freeform's upcoming TV series, "Shadowhunters." Katherine McNamara, Dominic Sherwood, Harry Shum, Jr., Alberto Rosende, Matthew Daddario, Emeraude Toubia and Isaiah Mustafa were psyched to surprise the fans with an impromptu holiday party after watching their submission videos.

"We watched the videos last night, and it was crazy to see how much these characters mean to them and inspire them every day," Emeraude Toubia (Isabelle) told MTV News.

Even though the show has yet to premiere, the cast already feels embraced by the fandom. "We find out everything from the fans," Alberto Rosende (Simon) added. "When new photos are posted, when new details are announced -- they know it first, and then they tell us."

"It's kind of nice," Dominic Sherwood (Jace) added. "It's like having little private detectives that work for us." Isaiah Mustafa corrected, "A league of spies."

For the fans, the feeling is mutual. "It feels like they're our friends," winner Victoria Buckley, 18, told MTV News after meeting the cast. "We wish they were our friends!"

Naturally, fans flipped when the cast entered the festively decorated room. (There was a cozy fireplace made entirely out of "Mortal Instruments" books!) It was the most magical moment of the night, as the fans excitedly posed for selfies and chatted with the cast.

"When I met Harry, I told him, 'You are taller in person!'" Tatiana Rodriguez, 16, said. "And then Alberto sat next to me, and my life was complete. It was amazing. It was a once-in-a-lifetime opportunity."

When asked what makes the "Shadowhunters" fandom so special to its fans, there was an overwhelming sense that there was a community here that was supportive, ravenous and encouraging.

"I've met international friends that are there for me more than real-life friends," Emily Utsch, 32, who called the "Shadowhunters" fan experience the third most special moment in her life, "after getting married and having my babies."

"Some of my other friends, none of them read books, so I was alone," Buckley added. "I didn't have anyone to fangirl with, and then I met all of my 'Shadowhunters' friends, and I finally felt like I met people who were like me. It makes me emotional just thinking about it."

And their passion hasn't gone unnoticed by the stars of "Shadowhunters."

"It's a different type of fandom," Harry Shum, Jr. told MTV News. "I never knew about fan fiction and all that stuff until 'Shadowhunters' came about, so it's an intense group of fans. They're really hardcore. They know the characters, I think, sometimes, better than we do. It's theirs more than ours."