The royal who married a divorced American is King Charles III. He married Camilla Parker Bowles in 2005, who was previously married to Andrew Parker Bowles.
This marriage caused controversy because of Camilla's previous marriage and the fact that Charles was previously married to Princess Diana. Diana's death in 1997 further complicated the public's perception of Charles and Camilla's relationship.
Despite the initial controversy, Charles and Camilla have been happily married for many years, and Camilla is now the Queen Consort.