Soon-Yi Previn might be the most infamous mistress ever. Woody Allen was her sort-of stepdad and married to her adoptive mother Mia Farrow when their relationship was discovered.
Camilla, Duchess of Cornwall
No THIS is the most infamous mistress ever: Camilla, the Duchess of Cornwall, was the very, very public mistress of Prince Charles while he was married to Diana. The two married in 2005 after Diana's untimely death.
Yep! Alicia Keys was a mistress before she became Swizz Beats baby mama.
When Jennifer Lopez started dating Skeletor (Marc Anthony), he was still married to Miss Universe.
Traci Lynn Johnson
Tiki Barber left his wife, who was pregnant with TWINS, for Traci Lynn Johnson.
Melanie Griffith and Antonio Banderas were BOTH married to other people when they got together in 1995. While there are reports he's still a cheather, they're still married almost 20 years later.