Khloé Kardashian joked about incest after brother Rob claimed her as his "crush" on Wednesday.

Rob kicked off October by celebrating the trending Women Crush Wednesday -- tweeting a screenshot of Khloé "arriving at a gym in Beverly Hills" on Tuesday, originally posted by Instagram user kuwtkgirls. The image sees the 30-year-old reality star showing off her derriere under a pair of tight, sheer black leggings. 

Shortly after, Khloé also took to her Instagram account to show her love for younger sibling. Well, too much love: she took the joke even further to the point of incest. She uploaded the screengrab of Rob's tweet, adding her own hilarious caption. "Totally a normal brother/sister relationship," she wrote. "Incest is best!!! #HeyBooHey."

It is certainly not the first time the Kardashian siblings have made crude jokes about their relationship. While guest hosting the late night talk show "Chelsea Lately" back in April, Khloé surprised the audience with her silly statement:

"Rob's been on my mind a lot lately because we're currently living together. And no, we're not sexually involved -- my brother's not nearly black enough for me!"

Khloé and Rob Kardashian, who are currently living together, have always been there for each other. "Rob and Khloé have always been tight. And Khloé has been there 100 percent for Rob since he's been going through hard times," a source told E! News.

"Also, Rob and [Lamar Odom] were really close, and after Khloé and Lamar split, it was so hard for Rob. He felt like he lost a brother that he had always wanted," the source continued. "Khloé knows how depressed he's been and is probably closer with him than any of her sisters."

"Rob also helped Khloé through the divorce with Lamar," the source added. "He was really there for her more than anyone."