Bruce Jenner's son has jumped to his defence following Jamie Foxx's transphobic joke at the iHeart Radio Music Awards.

Burt Jenner has lashed out at the 47-year-old singer-and-actor for poking fun at the former Olympian and his transition from male to female at the ceremony in Los Angeles on Sunday (29.03.15).

Speaking to TMZ.com, Burt said: ''I think he is just copying Kevin Hart because Kevin Hart is taking all his movie opportunities.

''He's copying him - man's on a roll and Jamie Foxx is on the way down. He's got his mojo going so he's got to copy what's working.''

Despite praising Kevin on his blooming career, the 36 year old also took a swipe at him for reportedly making a joke about Bruce's transition in front of his half-sister Kendall Jenner, 18, during Justin Bieber's Comedy Central Roast earlier this month.

He added: ''[Hart] did it in front of my sister [Kendall Jenner] -- he got lucky. He can make jokes about my dad all he wants but he can't make jokes in front of my sister and make my sister feel awkward. I would have charged the stage. If security got to me beforehand, I would've thrown something at him.''

Meanwhile, Jamie's controversial opening monologue appeared to fall flat with the audience - which was expected to include Bruce's daughter Kylie Jenner - failing to laugh and his remarks instantly attracted a barrage of criticism on Twitter.

Blogger Perez Hilton wrote: ''Boo! Shame on you #iHeartAwards for allowing @iamjamiefoxx to be transphobic on national television! Those #BruceJenner jokes were wrong!!! (sic)''