"We're just trying to not look back," says Brandon Jenner in new footage from his father's interview with Diane Sawyer

ABC Breaking US News | US News Videos Though Bruce Jenner currently enjoys a tight-knit relationship with his six biological children, that wasn’t always the case.

In previously unaired footage from his bombshell 20/20 interview with Diane Sawyer, Cassandra Marino, 34, revealed that her father “disappeared” out of their lives when they were young.

“Yes. The big formative years for them, I was really struggling with these issues [of gender identity],” Bruce, 65, told Sawyer, adding that he “didn’t do a good job. And I apologized for that.”

It seems to be water under the bridge for Brandon, 33. Sitting next to his father on the couch in Bruce’s Malibu home where the bulk of the interview took place, he said: “In seeing him come out to me and explain his true self, I was more proud right then to carry the last name Jenner, to be a part of the family, than at any time before.”

Burt, 36, is similarly forgiving. “The one thing that I think that we have gained that means more to us than anything is the honesty,” he said, to which Cassandra added: “I personally hope that this journey leads to the place that he wants it to.”

Jenner’s entire family has come forward in a show of support, including his stepchildren.

“Bruce is the most honest. … He has the biggest heart, and I’m really happy for him that he is living his life the way he wants to live it and that he has found inner peace and just pure happiness,” said Kim Kardashian West in a taped segment on the Today show Monday.

“That’s what life is about,” she said. “I don’t know what life would be like if you always felt like you weren’t yourself.”

Bruce Jenner’s Journey to Transition