The Most Controversial Royal Wedding Guests

In 1973, Greece voted to abolish the monarchy. Six years earlier, King Constantine II fled the country after backing a military coup, leading to widespread protests and backlash. Thereafter, he went into exile in the U.K., settling in London and remaining friendly with the British royal family. The Hellenic state may have ousted the monarchy, but that didn't stop the deposed royals from retaining their regal titles.

Accordingly, this caused controversy on Charles and Diana's wedding day in 1981. Constantine was close with Charles and he was, naturally, welcomed to the erstwhile Prince of Wales' big day. His invitation to the much-hyped wedding angered the then-president of Greece, Konstantinos Karamanlis, who refused to attend the ceremony out of protest. "The President of Greece did not attend because former King Constantine of Greece, a cousin and friend of Prince Charles, was invited to the wedding with the title of 'King,'" historian Carolyn Harris told History.

Constantine's decision to retain the title of king may have angered Republicans, but the former monarch eventually accepted that his kingly status was merely nominal. "I don't have to be in Greece as head of state. I am quite happy to be there as a private citizen," he told The Telegraph. "Forget the past, we are a republic now. Let's get on with the future."