READ: Taylor Swift Sings Beautiful Tribute to Jimmy Fallon's Mom on The Tonight Show

Monday was Jimmy Fallon's first day back hosting The Tonight Show after his mother, Gloria, passed away earlier this month. Taylor Swift was the guest singer that night, and she surprised everyone with the debut of her new song, "New Year's Day."

It was an incredibly emotional performance, as you can see below:

Mike DiCenzo, a writer and producer on the show, took to Twitter to share more of the story of what happened during the taping that day.

Take it away, Mike...

"It was our first show back after Jimmy's mom passed away...

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."

"They talked on the phone every day.

As Jimmy said, she was his biggest fan.

And as Questlove Gomez said, Jimmy is not only our boss, he's our family. We love him. So we were devastated for him last week, and we were feeling for him today."

"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.

But at the desk, you could hear his voice break when talking about our musical guest Taylor Swift, and that's because he knew what he was about to say..."

"Jimmy's words about his mom were beautiful.

'Mom, I'll never stop trying to make you laugh. I love you.' I was crying. We all were.

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."

"First, a quick word about Taylor Swift.

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.

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."

"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."

"Thank you to Taylor, the Roots, Higgins, our whole staff and crew, and to all the FalPals, fans, and everyone who reached out to and supported Jimmy and his family. I can tell you it meant everything to him.

One last note: our show was right on time today, but we edited out a minute to leave room for Jimmy high-fiving audience members during the end credits. It was Gloria's favorite part of the show."

"We love you, Gloria."

Many on Twitter shared the sentiment and sent their love to Jimmy:

And were incredibly moved by Taylor's performance:

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h/t: Twitter