Rob says it was all a “miscommunication” on his end.
The dad-to-be says it was all a “miscommunication”, stemming from him mistakenly believing that his family hadn’t invited his fiancée Blac Chyna to a planned baby shower.
Rob Kardashian has apologised for tweeting Kylie's phone number.
"It was miscommunication on my end," he told on On Air With Ryan Seacrest, Friday . "I thought they weren't having Chyna at our baby shower.
“Chyna's baby shower is actually this Sunday, but they were trying to do a little surprise 'guy' baby shower for me and I was just upset trying to fight for Chyna like, 'Yo, she has to be at the baby shower. She's birthing my child. She needs to be there.'
"It was literally miscommunication and I probably shouldn't have went on Twitter, but I did,” he admitted.
Rob added that he was mad at his whole family and didn't think at the time that tweeting his 19-year-old sister’s number was a big deal.
Kylie is said to have now changed her cell phone number and hasn't given her new digits to Rob just yet.
"We all love each other and we're all family and I never want to beef or argue with anybody," added. "I'm sorry, Kylie, if you're listening. I love you, Kylie."
Rob also quashed rumours that he and fiancée Blac Chyna, who was with him during the interview, have split. "We've been together the whole time, so I can't stand when people run stories like that," he said.
"Honestly, I didn't even know we were split up...I thought they were talking about me going in on my sister on Twitter or something like that,” he added.
“I’m very big on family. I always want to be with Chyna and I want to have more kids, so I don't like when I hear those types of stories."