Rex is Latin for King, Regina is Latin for Queen.

I don‘t know when exactly it became common practice in Europe, but it seems to be a very old tradition, as the user before stated, that earrings were common in the Minoan civilization already. In medeival time, it was common for both genders.

Interesting anecdote: Ever heard the German term ‚Schlitzohr‘? It translates to ‚rascal’, but the original meaning is ‚slit ear‘. It was tradition for master craftsmen and merchants to wear earrings as sign of their respectability. When they were caught cheating their customers, the earring was ripped off as a punishment. The slit ear showed that they are dishonest persons.

1917 the British royal family took over the official family name Windsor, which was used by all family members, who are not a ‚His/Her Royal Highness‘. In 1960, the name was changed to Mountbatton–Windsor for the descendents of Queen Elisabeth and Prince Philip. For example, Prince Andrew, Duke of York, and Anne, Princess Royal, children of Queen Elizabeth II, used the surname Mountbatten-Windsor in official marriage registry entries in 1986 and 1973 respectively. The queen or king will not use the family name. The former queen signed as Elizabeth R, the current king signs as Charles R (R for Rex/Regina).