Caitlyn Jenner shares the 'uncomfortable' secrets of her sex life with Kris Jenner.

When Caitlyn Jenner was introduced to the world in 2015 via an instantly iconic Vanity Fair cover, it was seen as a significant social leap toward transgender acceptance, a public triumph for those their gender identity.

But privately, the lead up to that moment, to personal acceptance, had been a struggle for the former Olympic decathlete and for those around her.

In her upcoming book, The Secrets of My Life, Caitlyn writes of the impact her gender dysphoria had on her relationship with her third wife, Kris Jenner, 61.

“We fall in love quickly (we marry after seven months),” the 67-year-old writes, according to People. “Since — let’s not kid ourselves — everyone wants to know, Kris and I have good and frequent sex at the beginning.”

Yet while Caitlyn reportedly claims that their physical relationship was “imbued with love”, she admits she wasn't ever "entirely comfortable" sleeping with her wife.

"I tell Kris about my gender issues before I make love to her. This will always be a subject of dispute between us,” the book reads. “She insists that she was taken by surprise by my ultimate transition to Caitlyn, which obviously means in her mind that she did not know enough.”

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Caitlyn, who has begun gender reassignment surgery, told People in an accompanying interview that she first experienced gender identity issues as a child in the '50s and '60s.

It was a time when such things were not spoken about, when - as Caitlyn said - "there wasn’t even a name for it".

So for decades she hid, until during her 24-year marriage to manager and Kardashian matriarch, Kris, things began to change.

“Outwardly, my life is good: terrific children, a strong marriage…, steady work... It's not enough," she writes, according to People.

“I keep [makeup how-to] books, along with my meagre collection of clothing, in a small closet with a lock in the back of my closet. Kris and I have negotiated this, since she is terrified, as I am, of the kids finding something.”

Eventually they did, and so did the world. And the post-transition Caitlyn is much more "happy and peaceful".

“I am ready to seize the day after so many years in which I just wanted the day to end,” she writes in the book, according to People.

“Life’s wonderful when you don’t have to lie to anyone and your heart is open.”

Kris Jenner has not publicly commented about the contents of The Secrets of My Life, which is due for release on April 25.