The 25-year-old model first had some fun with momager, Kris Jenner, when she called Kris, claiming that she was pregnant. Kendall is the only one of her siblings not to have a child.
"So, I have a scenario. I have not gotten my period in a little while and I was supposed to get it last week so I was kind of nervous and randomly took a test," Kendall begins. "And It came back positive so I took another one and that one also came back positive and I am literally about to cry."
Kris then says she had a dream in which her daughter was pregnant the night before.
"Really? I'm kind of freaking out. I just don't know what to do," Kendall continues the prank.
"Well, I'll put on my clothes and get over there. I'll tell you, Kendall, you know, you have to do whatever your heart tells you to do," Kris says. "I think it's great news, but I'm your mom."
Kendall couldn't keep it up any longer and finally comes clean, telling Kris, "I love you, and I loved your reaction."
"Oh brother, OK, I'll go put the champagne back on ice," Kris quips.
Kendall is then dared to tell her family that she's engaged to her NBA player boyfriend, Devin Booker.
"It's believable, so I will do it," Kendall says of her romance, which ET has learned is getting more serious.
She then texts the family group chat showing off a producer's engagement ring and pretending it is her own.
Sister Kylie Jenner immediately FaceTimes her and knows it isn't real, noting that the ring doesn't fit on her finger.
Kim Kardashian West also calls and isn't buying it after she sees that Kendall is at home.
A source previously told ET of Kendall's current relationship, “Kendall is usually super private, much more so than her sisters, but she’s really happy with her relationship with Devin and doesn’t care who knows."