On his first show back since the passing of his mother, Gloria -- who passed on Nov. 4 at 68 years old -- Fallon took time at his desk to remember his biggest fan.
"When we were little, my mom would walk us to the store -- me and my sister -- and we would hold hands. She would squeeze my hand three times and say, 'I love you.' And I would squeeze back, 'I love you, too,'" he said. "Last week, I was in the hospital and I grabbed her hand and I squeezed, 'I love you.' I just knew we were in trouble."
Swift -- who according to writer and producer Mike DiCenzo, was not originally scheduled to perform on last night's show -- was the musical guest. She sat at the piano and played "New Year's Day," off her newly released sixth studio album Reputation. One of the song's lyrics even nodded toward Fallon's earlier story about his tradition of squeezing each other's hands with his mother: "Squeeze my hand three times in the back of the taxi."
Watch the performance below: