These were some of the most famous and creative relationships in the history of art, driving each individual to heights of creativity and inspiration - and provoking them to despair, jealousy and betrayal. Matisse's success threatened Picasso so much that his friends would throw darts at a portrait of his rival's beloved daughter Marguerite, shouting 'there's one in the eye for Matisse!' And Willem de Kooning's twisted friendship with Jackson Pollock didn't stop him taking up with his friend's lover barely a year after Pollock's fatal car crash.