Kendall and Kylie Jenner are reportedly worried that people will bully Bruce Jenner, after the former Olympic athlete completes gender affirmation surgery.

According to Hollywood Life, the 65-year-old TV personality's youngest daughters are concerned for their dad.

"Kylie and Kendall are not worried for themselves, but they are worried that people will make fun of their dad. They want to protect him," a source told the website.

"Bruce has everyone's support. His family, both on the Kardashian side and his kids will support his transformation 100%. His kids are fine, they've known about this for quite some time now. This is new news to the public, but not to the family," another insider added.

Last February, Bruce Jenner checked into Beverly Hills Surgical Center for a laryngeal shave – surgery to reduce the appearance of the Adam's apple – sparking rumours that the former decathlete is transitioning from the male to female gender.

People later reported that a source close to the Kardashian-Jenner family had confirmed the rumours were true.

"Bruce is transitioning to a woman. He is finally happy and his family is accepting of what he's doing. He's in such a great space. That's why it's the perfect time to do something like this," a source said.

"He's being very smart about and also respectful about his transition," the insider added. "Instead of completely shocking everyone, his changes have been subtle, and his family has had the chance to slowly get used to his new looks and life."