#12 Taylor Momsen & Leighton Meester - Gossip Girl
The two main cast members of the Gossip Girl series, Taylor Momsen and Leighton Meester, initially had a good relationship on the TV show. After some time, the two had a falling out when the Gossip Girl production team began using Leighton's music instead of Taylor's. Leighton's songs "Good Girls Go Bad" and "Somebody to Love" were featured several times in the series, while Taylor's songs were not. Eventually, the two began to feud, and their friendship ended.