Brad Pitt & Angelina Jolie
And lest we forget the biggest relationship bombshell to rock Hollywood. Brad Pitt and Angelina Jolie fell in love on set while filming Mr. & Mrs. Smith back in 2004. As we all know, he was married to Jennifer Aniston at the time. Alas, you cannot stop fate, or Brangelina (although after 12 years, and approximately 20 children, the pair called it quits in 2016).