This is no wardrobe malfunction.

In celebration of passing 40 million followers on Instagram, Kendall Jenner shared what she calls "my favorite photo of myself," adding, "genuine happiness...taken by lil Ky."

(Warning: NSFW)

WATCH: Kendall Jenner Celebrates Her 20th Birthday in the Sexiest Jumpsuit We've Ever Seen

The reality star just turned 20, and her friend, Cara Delevingne upped the NSFW ante by posting a picture of Kendall's birthday cake, captioning it, "A CaKe for my CaKe."

(WARNING: Photo contains suggestive material)

WATCH: This Is What Kendall Jenner Would Look Like Pregnant

Kendall threw a big ol' party at The Nice Guy bar in West Hollywood, California, for her big day, where the model wore perhaps the sexiest, lowest cut jumpsuit in existence. Kim, Kourtney and Khloe Kardashian, as well as momager Kris Jenner, arrived in all-black outfits. Kris was joined by her boyfriend, Corey Gamble, and Kim's husband, Kanye West, also showed up. Kylie Jenner wore an orange jumpsuit for the occasion.

EXCLUSIVE: Kendall Jenner Explains Why She's Never Publicly Dated Anyone

While the 20-year-old has been in the spotlight most of her life, she opened up to ET exclusively in September about why she's never publicly dated anyone.

"It's not always easy, but I don't know, I just like to keep my private life private," Kendall said. "I try my best, but at the same time, I try not to let being out with someone affect my everyday life."

Watch Kendall stun at her 20th birthday party below!