Kevin Federline writes in his new memoir that he was never “against” his ex-wife Britney Spears, and he only ever wanted her to have an “incredible relationship” with their sons, but her allegedly erratic behavior made them wary of being around her.

In “You Thought You Knew,” out Oct. 21, Federline describes a particularly alarming situation described by his sons, Sean Preston, 20, and Jayden James, 19, when they were teenagers, according to portions of the book excerpted in the New York Times Tuesday.

“They would awaken sometimes at night to find her standing silently in the doorway, watching them sleep — ‘Oh, you’re awake?’ — with a knife in her hand,” Federline writes, according to the New York Times. “Then she’d turn around and pad off without explanation.”

Such alleged behavior has

See Full Page