The 28-year-old sock designer has seen his weight balloon since he ended his relationship with the Poison hitmaker in 2012 and his older sister has poked fun at the way his body art - which he had to cover up an inked tribute to another former lover, Adrienne Bailon - has distorted as a result.
Speaking on the latest episode of Keeping Up With the Kardashians, Kim said to her mother Kris Jenner and half-sister Kylie Jenner: "He covered the tattoo with a life-sized barbie doll of Rita that has now turned into a Cabbage Patch Doll.
"Have you seen it lately? It was like a Barbie doll and he's gained weight and it's like a huge Cabbage Patch Kid. Huge!"
The brunette beauty - who reportedly weighed 190 pounds while pregnant with son Saint - made the comments in scenes shot for the E! Show before Rob was rushed to hospital with health problems over the Christmas and New Year period.
Doctors discovered he has diabetic ketoacidosis. He has reportedly been instructed to eat well and exercise to get the condition under control and potentially into remission.