Rob Kardashian
Rob Kardashian is being linked to Karrueche Tran (not pictured) after he posted a screen grab of their text conversation. Reuters

Rob Kardashian, who has been working out hard to get back in shape, poked fun at his weight gain Thursday, by posting an old photo of himself sipping milkshakes.

"Started right here with these milkshakes #throwbackthursday," the former “Keeping Up With the Kardashians” star captioned the photo, hinting at his weight-gain struggle.

The 28-year-old reality TV star is getting back to his normal life and has started sharing several photos since returning to Instagram on July 31 with a shirtless throwback photo, following his excessive weight gain.

A source told E! News Thursday that "for the first time in a long time Rob is committed to changing his diet habits," and "he's been working with a chef and doing really well" so far.

"His regimen involves more than just cardio and weights," the source reportedly added. Rob has been working with his personal trainer, Gunnar Peterson.

On Tuesday, Rob posted a photo of sister Kylie Jenner and her rapper boyfriend Tyga on social media, along with an update of his workout.

“Spotted these fools on the morning workout,” Rob wrote, referring to Jenner and Tyga.

Meanwhile, Rob’s sister, Kim Kardashian West, also has been working out with him. Earlier this month, Kim said that she went on a tough hike with her younger brother.

Rob has been facing some major fitness issues in the past couple of years, and his mother Kris Jenner also addressed his weight issues in an episode of “KUWTK,” saying he gained over a 100 lbs. in a span of only a year.