As the rest of the high nobility in Flanders, Floris was a strong opponent to Cardinal Granvelle.
In April 1566, he was sent by the Council of State with John IV of Glymes to Spain in a last attempt to avoid war. As Glymes was wounded on the leg before leaving, Floris travelled alone. When the Beeldenstorm raged across the Low Countries, Floris was arrested and kept in house arrest in the castle at Simancas. When Egmont en Horn were arrested in Brussels, Floris was also condemned to death by the Council of Troubles. Instead of returning him to the Low Countries for his sentence to be executed, Philip II of Spain had Floris strangled in secret despite the pleas of his new wife Anna of Austria to release Floris, and spread the rumor that he had died of disease.