Splash News 1 / 12

He's coming back! Rob Kardashian has been out of the public eye for nearly a year and a half, with the exception of a few grainy paparazzi photos, but he's preparing to make a big (read: thinner) comeback.

Us Weekly is reporting that the reclusive Kardashian sibling has been hitting the gym hard and has already lost 15 pounds. The mag also claims that Rob has packed on 100 pounds within the past year.

"Rob has been sticking to the plan Gunnar [Peterson] created for him, and is getting meal delivery from a chef," a source said.

Over the past week, the former reality star has posted two photos of himself to Instagram, though it's not exactly known if they are current images or throwback photos. "Gnight," he captioned one of the selfies. The snaps show him now looking noticeably thinner than he was when the last public images were taken of him in June.

To get back into shape, Rob has working out with sister Kim Kardashian, according to their Twitter pages. On Aug. 14, Kim tweeted about going on "the hardest hike ever" with Rob, who then responded with, "GOOD work gurrrrrrllllll!!"

A few days later, he posted a photo of little sister Kylie Jenner and her boyfriend Tyga whom he spotted while getting his fitness on.

Aside from his health, the magazine reports that Rob has a huge incentive to get back in shape: cold hard cash from E! for his participation in the family's reality show, a show he hasn't appeared on since 2012.

"He's not getting paid if he doesn't film," another source said, adding that Rob has already started filming scenes for Season 11. "He has a $2 million-a-year contract. He realized he couldn't give up this huge opportunity."