Hilary Duff, Aaron Carter, and Lindsay Lohan
This early-aughts love triangle began in 2001 when Aaron Carter and Hilary Duff got together. The singer appeared on Lizzie McGuire Christmas special and became Hilary's on-screen (and off-screen) boyfriend. Behind the scenes, however, Aaron had his sights set on someone else.
"I was dating [Hilary] for like a year and a half, and then I just got a little bored, so I went, and I started getting to know Lindsay," Aaron told reporters in 2005. He dated Lindsay Lohan for a number of months before returning to Hilary. Eventually, the two called it quits because Aaron couldn't remain faithful, igniting a rivalry between Hilary and Lindsay that lasted for years.