Bruce Jenner's sons are supportive of their dad's transitioning.

Bruce Jenner

Bruce Jenner

Burt, Brandon and Brody reportedly "want to be there" for their father as he undergoes gender reassignment.

A source said: "The brothers just want to be there for their dad and to support him.

"They own the situation, and they aren't shy about talking about it."

Despite their previously "rocky relationship", the brothers are "cool" with their father's decision to transition to a woman.

The source added to PEOPLE magazine: "It was extremely hard for them to let Bruce back into their lives after barely having any contact with him after he married Kris.

"They can't believe that they finally got their relationship back on track, and now they have this crazy extra layer to deal with, but they love him and are cool."

Whilst Bruce's daughters Kendall and Kylie and step-daughters Kim, Kourtney and Khloe Kardashian are believed to be incredibly supportive of their father, Bruce's gender transition is a "hard pill to swallow" for ex-wife Kris Jenner.

An insider said previously: "(Kris) just couldn't emotionally handle it all when he finally came out with it. Regardless of whatever signs there were, it's a really hard pill to swallow. She truly went through a mourning period. And they really don't talk now."