Caitlyn Jenner shocked the world on Monday when she made her debut on the cover of Vanity Fair's July issue, but her stepson Rob Kardashian had no clue who she was at first glance.

Kim Kardashian sent a photo of Caitlyn to her family in a group text message. She and her sisters all knew about the photo shoot except little brother Rob.

"It was so funny because all the girls, we knew that Caitlyn was shooting this but my brother had no idea," Kim told Access Hollywood at the CFDA Awards in New York City on Monday. She sent the mass text, which included Rob, "and he goes, 'Kim, why are you sending me this? Who is this woman? And why do I care?' And I was like, 'Rob, that's Bruce! That's Caitlyn!'"

Once he got a better look, Rob couldn't believe his eyes.

"He was like, 'Oh, my god! She's beautiful!'" Kim said. "And then he called her and they had a love-fest and it was so cute. But the moment was so funny."

The 34-year-old reality star also helped Caitlyn, formerly known as Bruce, prepare for her big day with a few tips on how to look great for the cameras.

"Practice by yourself to figure out how you feel most comfortable," Kim told her. "She figured it out! It looks amazing."

The hairstylist Oribe, who did Caitlyn's hair for the Vanity Fair shoot, also did Kim's look for her recent Glamour cover. The expectant mother praised Caitlyn's first cover.

"She looked so beautiful," Kim told E! News. "I'm so proud of her and she's so inspiring. She wants to help others and get a good message out there."