Rob Kardashian’s bills are spiraling out of control, so he’s hitting up his billionaire sister Kylie Jenner for some much-needed cash, RadarOnline.com has exclusively learned.

“He’s taken so much off his mom and Khloe over the years, so it’s been agreed far and wide that it’s Kylie’s turn to help Rob out,” an insider explained.

But giving Rob a helping hand financially isn’t a totally selfless move on the family’s part.

“Everyone’s united in helping him get full custody of Dream, if only to stick it to Blac Chyna, whom they all loathe with a passion,” revealed the source.

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As Radar previously reported, Rob, 32, and Blac, 31, are locked in a bitter battle over control of their daughter.

According to court documents filed on January 7, the concerned dad has asked a judge for full custody of 3-year-old Dream and he wants the court to order his baby mama to undergo drug testing “no less than 30 minutes before each visit with an agency that conducts and observed tests and provides immediate results as well as full laboratory analysis.”

He’s offered to pay the costs and asked that if Chyna tests “dirty,” her visits should be suspended until she is clean, the legal papers read.

He’s also requested that all her visits with Dream be in the presence of a nanny — one which Rob will select and pay for.

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But the former reality star’s bitter custody battle with Blac comes at a steep price, one which Rob can’t afford.

Kim will help if she has to, but since Kylie’s got cash coming out of her ears right now it seems only fair for her to dip into her pocket,” said the insider of the situation.

“He’s lucky to have this help because there’s no way he could afford the legal bills on his own,” added the source.

Rob’s request to have full custody of his little girl are set to be discussed with Blac and the pair’s lawyers in a closed-door hearing next month.