In a new memoir, Kevin Federline, the dancer, D.J. and ex-husband of Britney Spears, provides his perspective on their strained relationship, and says he is concerned that the decision four years ago to release the pop star from her conservatorship may have been ill-advised.

In “You Thought You Knew,” due Oct. 21, Federline, 47, charts his path from teenage knucklehead growing up in Fresno, Calif., to husband and father of two children with the singer.

He and Spears finalized their divorce in 2007 after three years of marriage and then began a prolonged, messy custody battle that ended in 2008. In his book, Federline recounts his version of that dispute and talks of Spears’s use of drugs and alcohol and angry outbursts during the late stages of their marriage.

In the 18 years since their split, Federline has observed his ex-wife largely from a distance as the pair co-parented. “We haven’t spoken in years,” Federline told The New York Times in an interview. But he writes about becoming increasingly concerned with what he describes as Spears’s erratic behavior, which he learned about mostly secondhand from their two sons, Sean Preston, now 20, and Jayden James, 19.

In one chapter, he recounts the time when the boys, as teenagers, declared that they did not want to go back to their mother’s house for several reasons, including fear.