Rob Kardahian is determined to lose weight after skipping sister Kim Kardashian's wedding so he wouldn't have to pose for pictures.

Celebrity trainer Gunnar Peterson reportedly told TMZ.com that Rob texted Peterson after missing the nups, saying he vows to go to the gym every day until he loses weight.

"Rob is locked and loaded," Peterson told TMZ.

A source told E! News that Kim and new hubby Kanye West "completely understand" why Rob, 27, didn't attend the wedding, which was held in Italy over Memorial Day weekend and attended by the rest of the Kardashian clan.

"He wanted to be there, but he was feeling so insecure and didn't want anyone to see him heavier like this," a source said.

Meanwhile, sources told TMZ that Rob has "become so insecure and depressed about his appearance, he refused to be in the family wedding pics." Rob has publicly discussed his struggles with weight loss on "Keeping Up With the Kardashian."

En route to Kim's wedding, which he ended up deciding to skip, Rob was photographed looking heavier than ever. The pics prompted a barrage of online hate, to which Rob responded via Twitter: "So i found out i was trending [online] for being fat... thank you all it really made my day :)."