Taylor Swift made an unexpected appearance on the Monday night (November 13) episode of The Tonight Show, which just so happened to be the first broadcast of the late-night show since the passing of Jimmy Fallon's mother, Gloria.

Just days after serving as the musical guest on SNL, Swift took to the late-night show and performed reputation's closing track, "New Year's Day," but the backstory behind the somber cut's performance is the real interesting part of her appearance. Mike DiCenzo, a writer and producer for the show, took to Twitter after the taping to share details from the emotional showing.

"It was a really tough day for our whole staff. A lot of us knew his mom  Gloria, and she was the best. The best. She loved the show, she loved all of us, and most of all, she loved Jimmy," DiCenzo tweeted. "I'm sure today was especially tough for Jimmy. The fact that he came out, stood there, and did a normal monologue for the crowd is a testament to how strong he is. . . .The story about his mom squeezing his hand 3 times to say "I love you"  when he was a kid, and then him squeezing her hand in the hospital - he hadn't told any of us that story... More on that in a second."

DiCenzo went on to explain that Swift was not scheduled to do the show, but the show crew reached out to her because she was in town and they wanted to do something special for their return showing. Unsurprisingly, Taylor said yes with zero hesitation.

"She sang 'New Year's Day.' No one had heard it. Suddenly she sings the line, "Squeeze my hand 3 times in the back of the taxi." I nearly gasped. Tears. I think everyone in the audience started sobbing," he continued. "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. Whatever you think of Taylor, she did something beautiful for  Jimmy and our show today, and we're forever grateful."

Read Mike DiCenzo's full backstory on Taylor Swift's performance below!

Photo: Getty Images