When Kevin Federline began dating Britney Spears he was still involved with the mother of two of his children, Shar Jackson claims in a new interview.
Jackson was pregnant at the time with her second child when Federline stepped out on her.
And Shar says the truth came out only after he flew abroad for a commercial - which became a month-long trip with Britney Spears - according to an Associated Press report.
Federline and Spears were wed last year.
Jackson, 29, and Federline have a 3-year-old daughter, Kori, and a son, Kaleb, born in July 2004.
Brit and Kevin now have baby Sean Preston.
"How do you call yourself a human being knowing that you put somebody else through that pain?" Jackson asks of Spears in the December issue of Sister 2 Sister magazine.
"That's a vicious cycle right there, man. We gotta break that."
Its unclear who "we" is but there are reports that Brit has booted Kevin from the Malibu crib until Kevin changes his ways.