Britney Spears is speaking out against claims made by her ex-husband, Kevin Federline, after he publicly expressed concerns about her mental health. Over the past week, Federline has been discussing his upcoming memoir, You Thought You Knew, and his concerns for Spears. Federline and Spears were married from 2004 to 2007 and share two sons, Sean Preston Federline, 20, and Jayden James Federline, 19."The truth is, this situation with Britney feels like it's racing toward something irreversible," Federline, 47, wrote in an excerpt of his book, viewed by The New York Times.