Bruce Jenner and Kim Kardashian Bruce Jenner and Kim Kardashian

In Keeping Up with the Kardashians: About Bruce, which airs tonight and tomorrow on E!, Kim Kardashian reveals that it took her mother Kris Jenner quite a long time to adjust to her ex-husband's revelation that he's transitioning.

"This is really hard for her," Kardashian says of her mother in a sneak peek from About Bruce.

Kris Jenner: I'm "really happy" for my ex Bruce Jenner

In the clip, which was taped before Bruce Jenner's interview with Diane Sawyer aired on 20/20, Kardashian tells her sisters: "She cries all the time and it makes me really sad. We should really appreciate all the things she does for us, because she does a lot."

Kris Jenner publicly voiced her support for Bruce after the 20/20 interview aired.

Watch a clip from About Bruce here:

Keeping Up with the Kardashians: About Bruce Part One airs tonight at 9/8c on E!. Part Two airs Monday at 9/8c.

Look back on Caitlyn Jenner's inspiring journey: