Kevin Federline claims he walked in on Britney Spears doing cocaine while she was still a breast-feeding mother during an explosive night that resulted in their divorce. In his upcoming memoir, You Thought You Knew, Federline, 47, recalls Spears, 43, showing up to a 2006 release party for his album, Playing With Fire, despite having previously told him that she would be staying home with their two sons, Sean Preston and Jayden James. "As we reached the top [of the venue], Jamie Spears, Britney's dad, was standing there," Federline writes.