Caitlyn Jenner hasn't spoken to Khloe Kardashian in two years.
The 68-year-old star hasn't been as close to Khloe, Kim and Kourtney Kardashian - who she raised as her own daughters during her 23-year marriage to their mother Kris Jenner - since her transition and relations have been "lost" since the release of her book 'The Secrets Of My Life' earlier this year.
She said: "I don't talk about that side of the family, I spent 23 years of my life with those kids it's difficult to talk about it. Terribly, terribly sad.
"I've lost all relationship with them, yes I don't talk to any of them anymore.
"Actually, it was Kendall's birthday party a couple of days ago and I went to the party and I hadn't talked to any of the kids on that side.
"Kris [in] probably a year, Kim probably nine months, Khloe, 33, two years - but she wasn't there - and Kourtney I haven't talked to her either."
But Caitlyn admitted she speaks to her biological daughters Kendall, 22, and Kylie Jenner, 20 - who she shares with Kris - "all the time", and insists the pair are the "only ones I am really concerned about".
Despite this, Caitlyn admits it "hurts" not talking to Khloe, Kim, 37, and Kourtney, 38, whose father Robert Kardashian passed away in September 2003.
She said: "The Kardashians ... I spent 23 years of my life car-pooling those kids around, taking care of them when their father died, I kind of took over the role.
"It's not even a problem I just don't communicate with the others like I used to.
"It hurts but it's not the end of the world, fortunately I have 10 children, every day of my life is filled with being with the kids, going to dinner and lots of stuff ... fortunately I have a lot of children."
Caitlyn admitted she did briefly interact with Kim at Kendall's party, and expects the sisters and her to make up at some point.
Speaking in an upcoming episode of 'Piers Morgan's Life Stories', she added: "She said 'hi', that was about it. But it's a start, we are a family and I am sure we will get together and solve our differences, it all has to do with what I said in the book."
The Kardashians were said to be less than impressed with Caitlyn's memoir, which was released in April, after she hit out at Kris - who she divorced in 2015 after just under 24 years of marriage - insisting she told her she dressed as a woman, and did so in front of her before her transition.
But the showbiz matriarch has previously called Caitlyn's claims into question, insisting "everything she said is all made up".
Speaking about the book to Kim and Khloe, Kris said: "Why does everything have to be that Kris is such a b***h and an a**hole?
"All through the book - Kris knew. Kris knew before I even made love to her. I'm like, 'What?'
"I've never been so angry and disappointed in somebody in my whole life. I'm done."