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.