Britney Spears

When: 2004

Who: Kevin Federline and Shar Jackson

Kevin Federline and actress Shar Jackson were settled into a comfortable life together in the early 2000s, and by 2004 the couple had one child with another on the way. Two kids, white picket fence, the whole nine yards­­—sweet life, right? Nah, not for K-Fed. He wanted out and focused his efforts on brokering a power move with Britney Spears. Despite the fact that he was a backup dancer, Federline managed to bag Spears, leaving Jackson in his dust. By July 2004, Spears and Federline announced their engagement after dating for roughly three months. 

Jackson later commented, "[It] wasn't like breaking up a relationship. It was like breaking up a family." If that isn't homewrecking, what is?