The 'Keeping Up with the Kardashians' star filed for divorce from the basketball player last December amid allegations he had been unfaithful, and she has now confirmed he was sleeping with someone else during their four-year marriage.
She told her sister Kourtney Kardashian: ''Do you know the interviews he's doing? Saying that being married to me were the best years of his life and that he is now wearing his ring.
''F**k your ring. You were wearing it when you were f**king someone too.''
The 30-year-old beauty - who is now in a relationship with rapper French Montana - also admitted she regularly lied to her family about Lamar's behaviour, and even covered for him on his birthday.
Speaking on an episode of 'Keeping Up with the Kardashians' which aired in the US last night (13.07.14), she said: ''The way I was living is not a way to live!
''I kept in hiding every time there was something going on. I would have to lie, or conceal, or cover up, and I'm so over it.
''Let me tell you something. Last year on my birthday I lied to everyone because I had to lie and say I was with my husband when in fact my husband was missing with another girl...I was alone and lied to everyone.''
Elsewhere in the episode, Khloe took her marital problems out on her mother Kris Jenner during a furious row when the showbiz matriarch tried to see the sportsman's side of things.
When Khloe told Kris she wanted to ''cuss the f**k out of'' Lamar for pretending to the press that their relationship was fine, Kris told her that he probably ''just wanted things to go back to the way they were.''
Khloe replied: ''You always will stand up for him, prompting Kris to say: ''I'm not taking his side, I'm not buying into what he's saying. I'm just telling you that I love him very much and I want him to be OK.''
The furious former 'X Factor' host then said: ''He's available if you want to f**k him and date him.''