Rob Kardashian's weight gain is the main reason why he’s rarely photographed in public, but the 28-year-old has been keeping up with his fitness according to celebrity trainer Gunnar Peterson.

Peterson who also works with Khloe Kardashian, revealed that Rob has been hustling to get back in shape after his depression and weight gain. It sounds like the former 'Keeping Up With The Kardashians' star is back on the right path.

Rob Kardashian's weight has been an issue not only to Rob, but to the whole family. He even missed Kim Kardashian's wedding to Kanye West and Kylie Jenner's 18th birthday because he was too bothered about the way he looks.

He normally shies away from the celebrity spotlight, but Rob is now on a mission to get back in shape after reportedly gaining 100lbs. lately and his personal trainer Gunnar Peterson has insisted the star is working hard at it.

Gunnar Peterson told People magazine that Rob has been working out regularly. “Rob is always in!” Peterson said. “He’s slammed schedule-wise and still makes this work.” He’s got his hands full with his line of socks, Arthur George Socks by Rob Kardashian, but still finds time to take care of himself.“Never worry about Rob,” Gunnar told People.

Rob himself is sharing his progress, posting a photo on Instagram of sister Kylie Jenner and her boyfriend Tyga, whom he ran into "on the morning workout."

Rob Kardashian's weight may not be a problem anymore in the future as he’s also been working out with sister Kim Kardashian, who tweeted on August 14: “Just went on the hardest hike ever today with @robkardashian” and shared again on August 25: “Rise & Grind! Workout time!!!!! With @robkardashian”.

For the past several years, Rob Kardashian has been something of a mystery. Rob Kardashian's weight gain is clear to everyone, but the reasons for it were never revealed.

Rob's family has spoken about him in vague terms, saying he's "not comfortable in his own skin" and that "he's going through a hard time now."

Khloe Kardashian said earlier this year that her brother is trying to get his "groove" back.

She said: "Rob definitely has his ups and downs, and he's been struggling for the past year and a half, maybe two years, which I think we've all had those times in our life."

"He's been doing better, but I want Rob to do consistently forever. So right now I'm really proud of him."