Bruce Jenner's eldest son, Burt, lashed out at on social media after his dad's Diane Sawyer interview, claiming there were people in the reality star's life that hadn't supported the 65-year-old's sex change until it was convenient.
Now RadarOnline.com can exclusively reveal that the biting comments were aimed at his step-mom, Kris Jenner, and half-sister, Kylie.
In the now-deleted tweet, Burt sniped: "Having a hard time not putting a few people on blast who were not supporters beforehand, but want to act like they were all along."
"Burt has never had any sort of relationship with Kris, and his half-sister, Kylie, is a stranger," a family source tells Radar. "From numerous conversations with his dad, Burt knew Kris didn't support Bruce's sex change, and he wanted to publicly say something without upsetting his father. Burt does his own thing and can't be controlled by anyone."
Adds the source, "It's hard for Burt to watch as Kris and the rest of her family now publicly support Bruce, when behind the scenes it's a totally different story."
While Bruce's four biological children — Cassandra, Burt, Brody and Brandon — all participated in the interview, Kris told their two daughters, Kendall and Kylie, that it would be horrible for the family if they appeared on-camera, according to Radar's sources.
"She doesn't want Kendall and Kylie to be sucked into the media firestorm of their dad's sex change," reveals one insider.
Watch: Bruce Jenner Claims Kris Jenner Saw Him Cross-Dress