"He's such a nice guy," the 30-year-old actress tells "Inside Edition" in an interview that was to air Thursday. "He's made some mistakes, but everybody else doesn't have the whole world pointing their finger at their mistakes."
Jackson and Federline, 28, are the parents of a 4-year-old girl, Kori, and a 2-year-old boy, Kaleb. They dated before he became involved with Spears, whom he married in 2004, while Jackson was pregnant.
Spears, 24, filed for divorce on Tuesday. She's seeking custody of their two sons, 1-year-old Sean Preston and Jayden James, who was born Sept. 12.
Federline, who's been making the rounds promoting his hip-hop debut, "Playing with Fire," counter-filed court papers Wednesday seeking sole custody and spousal support.
Jackson, who starred in TV's "Moesha" in the late '90s, says Federline does not pay child support to her. But, she adds, "He does pay for their school, and they go to a very expensive private school."
Celebrity divorces, Jackson thinks, are nothing to celebrate. "I don't understand why people take so much joy in other people's pain."