Photo by Andrew Lipovsky

Taylor Swift may have unintentionally delivered an extra-emotional performance on Monday night's episode of The Tonight Show, Jimmy Fallon's first night back after taking a hiatus following the death of his mother Gloria Fallon.

Swift gave an unannounced performance of her song "New Year's Day," from her newly released album Reputation. But she may have inadvertently delivered something more meaningful for Fallon as he continues to mourn the loss.

Mike DiCenzo, one of the show's producers, explained on Twitter that Swift wasn't scheduled to appear, but since she was still in town from performing over the weekend on Saturday Night Live, the crew reached out, explaining they wanted to do something special for Fallon. She quickly agreed.

While Swift performed single "...Ready for It?" and an acoustic version of her standout track "Call It What You Want" on SNL, she opted for the tender album-closer "New Year's Day" for Fallon.

Earlier in the show, Fallon took a moment to thank fans for their support and he recalled a childhood memory of his mom.

"When we were little, my mom would walk us to the store, me and my sister, and we would hold hands," Fallon explained. "She would squeeze my hand three times and say 'I love you,' and I would squeeze back, 'I love you too.' And last week, I was in the hospital and I grabbed her hand and squeezed ... and I just knew we were in trouble."

No one on the crew—and especially not Swift—knew about that story until Fallon told it. But coincidentally, "New Year's Day" includes the lyrics, "You squeeze my hand three times in the back of the taxi."

The song itself is already clearly a very personal one for Swift, but it also served as an unexpected tribute to Fallon's late mother. 

"I think everyone in the audience started sobbing," DiCenzo said of the moment Swift sang those lyrics. "I could see Jimmy silhouetted at his desk dabbing his eyes with a tissue. We all lost it. It was a beautiful coincidence in a beautiful performance. 'Hold on to your memories, they will hold on to you,' Taylor sang. That hug between Jimmy and Taylor after the song was 100% real emotion."

See video of Fallon's tribute to his mother and Swift's performance below.