Rob Kardashian has the biggest butt among the Kardashian siblings! LOL! That’s according to sister Kim Kardashian who is famous for her big booty! Kim tweeted about her brother Robert Kardashian’s bigger derriere via her Twitter account.

more photos of little brother Rob after the big derriere challenge…

Do you believe Rob has the biggest derriere? I seriously doubt it.

The Kardashians were at the Kardashian Charity Knock Out event where fans bid online to get them to box for charity. Kim was left with a black eye and poor Rob ended up in the hospital with a concussion! Ouch. Thank goodness he’s all better now.

Do you believe Rob has a bigger behind than any of his sisters? Hmmm!

photos: Fame