Jessica Wright, Lucy Mecklenburgh, Billie and Sam Faiers and Ferne McCann were on their way to a Calvin Harris gig when they spotted the US reality star.
The Essex ladies were glammed up to the eyeballs, however Rob was keeping it cool in a black T-shirt, black jeans and trainers and a blue baseball cap.
Gathering around Rob - who is the brother of Kim, Kourtney and Khloe Kardashian - the girls all pulled their best smiles as they got their photograph.
Lucy then shared the snap on Twitter, simply saying: "With @RobKardashian x"
The girls weren't the only ones rubbing shoulders with stars either, as Ricky Rayment also met Mike Tyson in Vegas last night!
After their encounter with Rob, the ladies headed to Hakkasan nightclub, in the MGM Hotel on the Strip, to watch Calvin.
Ferne tweeted: "Hakkasan tonight with my b*tches @lucy_meck @BillieFaiers @SamanthaFaiers @MissJessWright_ ..... @CalvinHarris we r coming to get u."
Later, Jessica shared a picture of herself and Lucy snuggled in bed together. She said: "Calvin smashed it but time to get beauty sleep."
Check out more pictures of the TOWIE stars in Vegas in our gallery!
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