Bruce Jenner may have openly discussed his gender transition journey during his tell-all interview with Diane Sawyer last month, but until now he has not discussed how his children and stepchildren took the revelation.

The first segment of a two-part Keeping Up With the Kardashians special, titled About Bruce, aired last night, and it shows just how tough the news was for the girls to take – and that more than one of them had always suspected something was going on.

Discussing Bruce's transition, mum-of-one Kim said that she had known since she was a child that Bruce enjoyed dressing in female clothes – and that she first became aware of his plans to change his gender over ten years ago.

"It's been kind of my job to keep this secret for over a decade," Kim told the cameras.

 

Tonight's episode of KUWTK is very emotional. Our hope is that other families experiencing similar situations as ours don't feel alone! Life is about love and acceptance and we all have our own journey! With support and love of others especially family anything is possible! Tune in to see our journey at 9/8 c on E!

A photo posted by Kim Kardashian West (@kimkardashian) on May 17, 2015 at 5:09pm PDT

For Bruce's stepdaughter Khloé and his teen daughters Kendall and Kylie, the most difficult part of the process was that Bruce was not totally up front with them about his plans.

During one tearful conversation, filmed in January 2015, Khloé is seen telling Bruce that it is his responsibility to tell the girls exactly what is going on. "I have always supported you, but I don't think it's fair that you won't tell us how close this is in the near future," she said of his reluctance to tell them when he would reveal his female identity to the world.

"There's no right way to do this," counters Bruce.

Pushed by Khloé, Bruce told his daughters that within five to six months, his new female identity would replace him.

Kylie in particular found the news difficult to discuss on camera. "He sat me down. He told me everything," she said, before becoming too emotional to continue.

As for Kendall, she admitted that she had always known something was going on but that she had never realised how far it went. "We'd find makeup, like lipstick, and we'd think he was having an affair and we didn't want our family broken up so we didn't tell anyone," Kendall revealed.

The 19-year-old model also recalled one incident when she saw Bruce dressed as a woman at home. "I woke up to go and get water and I came down the stairs and went into the kitchen and I saw him…. and I just backed up and I ran up the stairs quietly and I went to bed," she explained.

The second part of the KUWTK: About Bruce episode airs tonight.