"I'm so happy after such a long struggle to be living my true self. Welcome to the world Caitlyn. Can't wait for you to get to know her/me," he posted on his Twitter account.
His family has expressed their support for Bruce's transition.
"Be free now, pretty bird," daughter Kendall Jenner posted.
"Freedom. Stunning," Khloe Kardashian tweeted while posting a photo of Caitlyn.
Meanwhile, daughter Kim Kardashian urged everyone to follow Caitlyn on Twitter.
"How beautiful! Be happy, be proud! Live life your way. Everyone pls follow @Caitlyn_Jenner on Twitter," she posted.
In an interview on 20/20 with Diane Sawyer, Bruce admitted he is a transwoman. He also revealed crossdressing for many years but quit after meeting Kris Kardashian in the 90s.