The singer -- who has appeared on The Tonight Show several times in the past -- kicked things off with a pre-taped segment where she surprised her fans as they sang "One Last Time."
After the adorable segment, the 24-year-old pop star once again proved her sketch comedy chops (which she already demonstrated when hosting Saturday Night Live in 2016), in one of Fallon's famously odd skits, "NBD," where the pair played two aloof hipsters trying to one-up one another.
The big highlight of the night, however, came when the pair played "Musical Genre Challenge," in which they attempt to sing hit singles in a totally different genre.
Fallon tried his hand first, singing Ed Sheeran's "Shape of You" set to a ska beat -- courtesy of The Roots -- and, in a weird way, it was one of the better "Shape of You" covers that you're likely to hear.
However, that performance was blown out of the water when Grande stepped up and belted out a rendition of Kendrick Lamar's "Humble" in the Goth Rock style (or, as Grande put it, "like 2003 Evanescence goth" or "Hot Topic shopping goth").
Fallon followed that up with a Johnny Cash-style country ballad reimaging of Usher's "Yeah," before Grande closed the whole thing out with a bombastic performance of the Drake song "God's Plan" in the style of a '90s pop diva.
The singer also sat down with Fallon on the interview couch, where she opened up about her new music and her forthcoming album, which Fallon revealed is titled Sweetener.
The host asked about the album's title and what it means in terms of her upcoming music.
"Because it's kind of about bringing light to a situation, or someone's life, or someone who brings light to your life," Grande shared. "Sweetening the situation."
Every small detail Grande shared elicited wildly enthusiastic reactions from her fans in the audience.
"My album is coming this summer," Grande said, to a cacophony of cheers. Grande even hinted at a release date, telling Fallon that it will be coming out in around three months.
"Thank you for coming on our show and for being strong, and for entertaining," Fallon said, getting quietly emotional as he reflected on the incident. "And for going back to Manchester and doing a benefit, I thought that was awesome of you and I just think you're so strong, and so cool."
A somewhat somber Grande thanked Fallon for his kind words and became emotional while as he read an essay she'd penned about the tragedy.