The two models appear in a trailer for Apple Music’s Carpool Karaoke series, where they turn off the tunes to take a lie detector test while in the car.
Jenner, 22, starts off with some tame questions, asking her pal if she likes her hair up in a ponytail. Baldwin, 21, tells the truth, saying she does, which prompts Jenner’s response of, “Cute.”
Baldwin isn’t so easy on her friend, laughing while she asks, "Have you ever created a fake Instagram to look at what your ex-boyfriend is doing?”
Giggling, Jenner replies, "You know the answer to this! Yes!”
The Keeping Up With the Kardashians star has previously been linked to rapper A$AP Rocky, singer Harry Styles, and basketball stars Blake Griffin and Ben Simmons.
The best moment of the clip comes when Jenner asks Baldwin, "Does Justin think I’m cool?”
There’s a long pause as Baldwin decides whether to throw Bieber under the bus.
"Of course!” she replies, before the lie detector administrator declares this is a “lie.”
Getting back to the music, the pals then belt out a verse from Panic! At the Disco’s hit song, “I Write Sins Not Tragedies.”
Jenner is a longtime friend of both Bieber and Baldwin, opening up last month about the pair’s then-engagement on The Tonight Show Starring Jimmy Fallon.
“Whatever makes them happy, I’m happy,” she said. “I’ve been friends with both of them for a very long time. So everybody’s happy, and that makes me happy.”
The couple has been through their series of ups and downs since secretly tying the knot in NYC last month. Here's more on the pair: