Here's Why Taylor Swift's 'Tonight Show' Performance Made Jimmy Fallon Cry

The singer has been on a blazing trail of revenge (literally), but Taylor Swift surprised The Tonight Show on Monday night to sing a different kind of tune. Swift, who's promoting her new album (which consistently references her "big enemies"), changed it up with a much more emotional song. In the last-minute performance, Swift live debuted "New Years Day" and it will probably reduce fans to tears for an unexpected reason.

After the performance, which consisted of Swift, her piano, background vocalists, and a guitarist, the singer immediately got up and gave host Jimmy Fallon a long hug while patting his back. It wasn't just an ordinary hug, which Fallon's reciprocation and somewhat flustered face proved. If audiences were watching the episode from the beginning, they'd know why.

It was Fallon's first show since his mother Gloria passed away on Nov. 4, which he tearfully addressed at the beginning of the show. "She was the best audience. She was the one I would always make laugh," he said. But the host really began getting choked up when telling a short anecdote about his mother (one that also ties to Swift's ballad).

"When we were little, my mom would walk us to the store, me and my sister, and we would hold hands," he tearfully explained. "She would squeeze my hand three times and say, 'I love you.' And I would squeeze back and say, 'I love you too.'" The 43-year-old was barely able to get the words out explaining how he did the same thing while his mother was in the hospital on her death bed.

Swift's performance made the evening even more emotional, perhaps because of select lyrics that somehow perfectly tie into Fallon's story. "You squeeze my hand three times in the back of the taxi/I can tell that it's gonna be a long road," she sang. "Hold onto the memories, they will hold onto you."

Later, Tonight Show writer/producer Mike DiCenzo took to Twitter to explain how the performance came together last-minute for such a powerful moment. DiCenzo said it wasn't scheduled and Swift immediately agreed when asked on a whim. He also called Swift's song choice a "beautiful coincidence" that no one was prepared for, saying her hug with Fallon was "100% real emotion."

"I nearly gasped. Tears. I think everyone in the audience started sobbing," the producer wrote. "I could see Jimmy silhouetted at his desk dabbing his eyes with a tissue. We all lost it." Tonight Show's house performer Questlove was also astounded by the performance.

The performance certainly tugs at anyone's heartstrings, whether feeling for Fallon or having experienced something similar. And before the song's live debut, fans theorized about "New Year's Day" and who it could be about, many suggesting it's inspired by Swift's ex-boyfriend Harry Styles.

Another set of lyrics in the song are, "Candle wax and Polaroids on the hardwood floor/You and me from the night before." True Swifties know that Swift referenced polaroids in "Out of the Woods," which is also believed to be about the former One Direction member. There's also telling proof given the parallel to the song in One Direction's "Perfect" lyrics: "If you like causing trouble up in hotel rooms/And if you like having secret little rendezvous/Then, baby, I'm perfect for you."

And when really diving into the lyrics (because Swifties mean business), fans noticed Swift sings about someone's distinct laugh in the song. "Please don't ever become a stranger whose laugh I could recognize anywhere," she sings. Speculations include both Harry Styles and Swift's other ex-boyfriend Tom Hiddleston.

Regardless of who the song is about, it was able to really move Fallon in a way that was emotional and real, at a time when he needed it.