ANOTHER Kardashian has joined the list of Most Vain Americans!

At age 25, Rob Kardashian bought himself a youthful new look – thanks to his big sister Kim, say sources.

The ENQUIRER has learned that the former “Dancing with the Stars” finalist visited the offices of a top plastic surgeon that Kim highly recommended and ironed out his face with Botox injections.

“Rob was complaining about his face drooping and that he’s starting to look old,” a close source told The ENQUIRER. “Kim told him to stop whining and put his money where his mouth is.

“She turned him on to her trusted plastic surgeon and convinced him to go for a Botox treatment. Rob was all for it and made an appointment right away.”

His mom Kris and stepdad Bruce Jenner are plastic surgery veterans, and Kim 32, has admit­ted: “I’m totally not against plastic surgery” – so it didn’t take much to convince Rob to tighten up.

THE “KEEPING UP WITH THE Kardashians” star recently ended a romance with sexy British pop star Rita Ora, 22, after he claimed she cheated on him.

But right now his mind is on busi­ness. The one-time model-turned-entrepreneur recently launched a line of designer socks and wants to remain youthful in the eye of the public.

“Rob may be young, but he’s just as vain as his famous family,” said the source. “And it’s no secret he’s been pampered from birth. Rob loves to get manicures, pedicures, facials and skin treatments – he even loves bubble baths.

“His main concerns about getting Botox were having a stiff face that didn’t move and what his buddies would say.

“The doctor he went to was a pro. Rob’s face felt a little weird, but he walked out of the Beverly Hills office feeling like a new man and more confident than ever.

“It was just what the doctor – and big sis Kim – ordered.”