After the heartfelt performance, which featured Swift soulfully singing and playing piano, she shared a sweet moment with Fallon when he came over to her after the performance..
The two embraced in a long hug and Swift supportively patted Fallon on the back before the teary-eyed host thanked her for joining them.
At the start of the show, Fallon emotionally paid tribute to his mother with a tearful story about a particular childhood memory.
"When we were little, my mom would walk us to this store, me and my sister, and she would squeeze my hand three times and say, ‘I love you,’ and I would squeeze back, ‘I love you, too,'” the host recalled, as he struggled to hold back tears.
"Last week I was in the hospital and I grabbed her and squeezed 'I love you.' I just knew we were in trouble, you know? I feel so grateful to be able to do this every single night and I’m very appreciative of all the support from all of you that my family received over the past week,” he continued. "We’re going to continue to work really hard to bring some light and some laughter into the world. Thank you for watching, thank you for helping me and my family recover from this loss. Mom, I’ll never stop trying to make you laugh. I love you."
The sweet memory Fallon shared proved to be particularly poignant due to an incredible coincidence regarding the song Swift performed, which actually includes the lyrics, "You squeeze my hand three times in the back of the taxi."
DiCenzo took to Twitter to share a few words about Fallon's first show back, and give a little insight into Swift's involvement.
"She was not scheduled to do our show today. But we wanted something special for this first show back, so we asked her on a complete whim, since she had been in town doing SNL. She said yes with zero hesitation," DiCenzo wrote.
According to the producer, no one had heard "New Year's Day" before she played it, and they didn't know about the lyric beforehand.
"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 wrote. "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."
"That hug between Jimmy and Taylor after the song was 100% real emotion," he added. "Whatever you think of Taylor, she did something beautiful for Jimmy and our show today, and we're forever grateful."