The Olympian is set to tell his story Friday night in an interview with Diane Sawyer

Credit: Axelle/Bauer-Griffin/FilmMagic

As Bruce Jenner told the world he’s transitioning from male to female, his youngest daughter Kylie Jenner supported her dad on social media.

“Understandingly, this has been very hard for me,” she Tweeted on Friday night. “You will hear what I have to say when I’m ready to but his isn’t about me. I’m so proud of you, Dad. You are so brave. My beautiful Hero.”

Earlier in the day, Kylie, 17, posted a vintage photo of her father.

“daddy throwback. #Tonight #DianeSawyer #ABC #love,” she captioned the shot of Jenner wearing jean cutoffs and a t-shirt showcasing his toned stomach.

Jenner, 65, discussed his journey in a 20/20 interview with Diane Sawyer set to air Friday at 9 p.m. ET on ABC.

A source previously told PEOPLE that Jenner’s six kids and four step-children have rallied around the Keeping up with the Kardashians reality star.

“They all came all around pretty quickly, but each of them had to process it in their own way,” the insider said. “All they want is for him to be happy.”