Rob Kardashian just pointed out the culprit of his weight gain in a rare Instagram post as the former "KUWTK" reality star has hired a personal chef in order to drop the pounds.

Three days ago, Rob Kardashian shared a photo of back when he was still a few pounds lighter as he wrote, "Started right here with these milkshakes hahaha ... #throwbackthursday."

One of his followers wrote, "Why (is) he forever putting up old pictures.. Come on(.) (I)f your (sic) fat(,) no one cares lmaoo (J)ust be honest with yourself.. We dont care (if) u (sic) still got money n (sic) girls still want u."

Another said, "Would be an honour to meet you @robkardashian your (sic) an inspiration & I think your (sic) one of the strongest guys in the world!! I've been where you've been in the darkest of times & without all the extra stuff you have had going on makes me admire you so much more!! Love always."

And still another commented, "Im glad you are still here and letting those who care about you and your family, see your great sense of humor. Hoping and praying for the best for you. I cant imagine having to live under the scrutiny of the public eye, as your family has chosen to do. It takes strength to do both; be there for the world to be voyers Or to be strong enough to say no and protect your privacy and world. Bless you Rob. Be safe, and find wisdom."

E! News has reported that Rob Kardashian is really committed to do something about the weight gain, as the sock mogul reportedly ballooned to 300 pounds.

"For the first time in a long time Rob is committed to changing his diet habits," the source claimed.

"He's been working with a chef and doing really well."

Kim Kardashian earlier shared a photo on her Instagram showing her and her brother on a hike in California, proving that Rob Kardashian is indeed doing something about the weight gain.

Gunnar Peterson, Rob Kardashian's personal trainer, dished to E! News, "His regimen involves more than just cardio and weights."