Hot on the heels of his sister Kim’s “sham marriage” bust-up comes stunning revelation about “Dancing” bro’ ROB!

Is he or isn’t he gay? That’s what fans of “Dancing with the Stars” are asking about dark horse Rob Kardashian. Much to his aston­ishment, Rob’s suddenly waltzed his way into becoming a homosexual icon – and insiders say his sister Khloe ignited the gay fervor.

The playful Kardashian sister used Twitter to send sexy messages to the gay community – pretending they came from her brother!

Now gay websites are ablaze with racy comments about Rob, guys go ga-ga and hit on him, and celebrities – including Carson Kressley and David Arquette – make cracks about the reality star’s posh posterior.

“Rob can’t believe the attention,” divulged a close source.

The 24-year- old “Keeping Up with the Kardashians” star is flat­tered by the compliments from gay admirers.

“But privately, he’s worried it might give women second thoughts about him,” said the source.

“Rob definitely fancies himself a ladies’ man. He used to date The Cheetah Girls singer Adrienne Bail­on…until she caught him cheating with another woman.”

Rob – like his amply-endowed sister Kim – owes his pop­ularity in large part to his big butt, say sources.

Gay Internet sites are on fire with messages from fans – and have even posted a pic of Rob in his un­derwear. One admirer, writing on the gay Internet forum, declared: “It would be awesome to see this guy…clad in a pair of tight Levi jeans!”

Another poster agreed: “Rob does have a nice round (butt), especially in tight pants!”

Even Rob’s openly gay “DWTS” competitor Carson Kressley, who was recently voted off the competi­tion, has admired Rob’s posterior, cooing: “He has a fabulous rump!”

Another “DWTS” competitor, jokester David Arquette, went so far as to post a Twitter pic of Rob’s behind!

Rob owes the gay fascination with him to prankster sister Khloe.Insiders say she’s responsible for the fake posts on his Twitter page.

The first one read: “I love (men’s private parts).” Followed by: “Yum yum yum.”

The phoney Rob then started writing about his attraction to Khloe’s hus­band, Lakers star Lamar Odom. “I love my brother-in-law. He is so big and sexy.”

Alarmed, the real Rob took control of his Twitter page and tried to clear up the mess

He tweeted: “…That was my Sis @ KhloeKardashian! She was havin a moment!”

In the past, Rob has been targeted as gay by other pranksters.

Two years ago, a hoaxer changed his bio on Wikipedia to say he’s gay and had become a porn star.

Courtney Love once blogged that Rob had attacked a gay employee of hers at an L.A. nightclub – and im­plied that Rob is gay.

Concluded the close source: “Rob can’t win for losing! Either people think he’s gay or a gay-basher. And he’s neither!’”