Caitlyn Jenner has undergone sex reassignment surgery.

According to RadarOnline, the 67-year-old television personality - who was previously known as Bruce Jenner - reveals in her upcoming memoir 'The Secrets of My Life' that she had surgery in January 2017.

Caitlyn writes: ''The surgery was a success, and I feel not only wonderful but liberated.

''So why even consider it? Because it's just a penis. It has no special gifts or use for me other than what I have said before, the ability to take a whiz in the woods.

''I just want to have all the right parts. I am also tired of tucking the damn thing in all the time.

''I am going to live authentically for the first time in my life. I am going to have an enthusiasm for life that I have not had in 39 years since the Olympics, almost two thirds of my life.''

And Caitlyn also opens up about why she has finally decided to speak about the procedure, despite previously refusing to answer questions on the topic.

She says: ''You want to know, so now you know. Which is why this is the first time, and the last time, I will ever speak of it.''

Former Olympian Caitlyn revealed in a '20/20' interview with Diane Sawyer in April 2015 that she was transitioning.

She explained: ''For all intents and purposes, I am a woman.

''My brain is much more female than it is male. That's what my soul is. Bruce lives a lie. She is not a lie. I can't do it anymore.''

The 'Keeping Up with the Kardashians' star first announced she was working on the memoir in January 2016 and said the story would detail her ''journey from Bruce to Caitlyn, and her brave transition into womanhood''.

In a statement, she said at the time: ''Things have been moving so quickly that it will be nice to slow things down a bit and take the proper time to reflect on this journey.

''I couldn't pick a better team, in Grand Central and Buzz [Bissinger], to make sure this story is told with a lot of honesty and care.''

'The Secrets of My Life' will be released on April 25.