While Kourtney insisted that she's "just friends" with the 21-year-old pop star, Ellen wasn't so sure. "Why are you smiling that way?" the host quipped. "You're smiling as if that maybe it's beyond friends."
"I've been smiling this whole time since I've been sitting here," Kourtney responded.
"No, not like that. That was as whole different thing," Ellen joked.
Khloe Kardashian was later Facetimed into the conversation and Ellen sarcastically said that Kourtney had "went so far into detail" about her rumored romance with Justin. "I heard you know more about that than I would," Khloe responded.
See photos of Kourtney and her ex Scott Disick through the years:
Kourtney also commented on her sister Kendall Jenner's relationship with Harry Styles, and admitted that she still hasn't met the One Direction singer.
While Kourtney wouldn't confirm her sister's rumored romance with the heartthrob, Khloe told ET that the two are an item. "I don't know if they're like boyfriend-girlfriend," Khloe explained. "Nowadays I don't know. People are weird with stuff. So, I don't know their title. But I mean, they were in St. Barts together hanging out, so to me that's dating."
Here's more of ET's interview with Khloe: