The Dangerous Woman singer went back to her Broadway roots during a low-key gathering on Saturday night (30Jul16), and took to Snapchat to share videos of her and the Family Guy creator singing tunes from Rodgers and Hammerstein's Cinderella.
In the footage, Ariana and Seth are shown casually sitting near a piano and sharing a microphone as they harmonise and alternate between the lyrics of the musical's numbers Impossible; It's Possible and In My Own Little Corner.
Ariana also shared some clips on Instagram, alongside the caption, "I mean........ nothing like some sensible Rodgers & Hammerstein karaoke with Seth Macfarlane."
Ariana has been an unlikely fan of the actor/singer for years, and she took to Twitter in 2011 to praise the star after seeing him perform his big band music in Los Angeles.
"Last night I saw Seth MACfarlane sing hits from the 40s with an orchestra!" she wrote. "He was fantastic, I love his voice!"
Seth appeared to be a fan of Ariana's too, and invited her to make a cameo in a 2014 episode of Family Guy, playing a loud "Italian girl" living next door to the Griffin family.
The Cinderella karaoke served as a musical warm-up for Ariana as she's gearing up to star in the upcoming TV production of Hairspray Live! as Penny Pingleton.
Ariana, who got her start in theatre and even performed in Broadway musical 13 in 2008, announced the news in July (16), and couldn't contain her excitement for the new gig in a series of messages on Twitter.
"Most of you know that I'm really just a musical theater geek. Like a really big one... so... my heart is very full re: this announcement. I AM NOWWW A CHECKERBOARD CHICK. Penny has been a dream role since Hairspray opened on Broadway. At 9, I was (and still am) in LOVE w (original Broadway cast member) @KerryButlerNyc. hope to make u proud (sic)."
"I'M GOING TO BE IN A SHOW WITH @HarveyFierstein AND @KChenoweth IS THIS AN ACTUAL JOKE...," she added. "I'm so honored and beyond excited to be a part of this dream cast... I will for sure pass out at the table read."
In addition to Kristin Chenoweth and Harvey Fierstein, Jennifer Hudson, Derek Hough, Martin Short, and newcomer Maddie Baillio will also star in the live show, which will air in America on 7 December (16).