"We were laughing so hard," Kim tells ET's Keltie Knight of the response to the tune. "The other night with her, we were like, 'How did this become a thing?' This is so funny to us -- all the memes that they were making."
Khloe agrees of the memes, adding, "It's so stupid funny."
While the origins of Kylie's "Rise and Shine" are unclear, Kourtney reveals that she has a ditty of her own. "I have my good morning song," the mother of three shares before her and her sisters start singing the tune.
"The sun is shining. Hooray, hooray. Have a good day, have a good day," they croon.
After the epic sing-along, Kourtney admits, "I sing that in the morning to all of them when I wake them up, but [my son], Reign likes the 'Rise and Shine.'"
In addition to creating the next viral sensation, the Kardashian siblings are currently collaborating on the KKW Fragrance Diamond collection.
"I love doing collabs with my sisters. It makes me feel kind of nostalgic," Kim tells ET of the perfume project. "We haven't really done anything together, the three of us in so long, at least for a decade... We kind of branched out and started doing our own projects, so to me, this was a no-brainer."
The KKW Fragrance Diamond collection launches on Nov. 8, and be sure to tune in toEntertainment Tonight for our full interview with Kourtney, Kim and Khloe.