During the Middle Ages when the Kings and other nobility committed a crime, they were treated very differently from the lower-class and peasants. When a King or royalty committed a crime, they were generally only given a fine. However, if a peasant committed a crime then they were tortured and punished, some of these punishments lead to death or permanent physical mutilation. The only way that a peasant could be given a fine was if they committed a very minor crime or if you had a powerful friend that could bribe the King, Gaoler, Judge. Etc.
However, if a King or Queen committed an exceptionally serious crime then they could be sentenced to death. Even then, though, they were not executed in the same way that a commoner would be. When the Royal "criminal" was executed they were beheaded- this was still a very painful way to die because sometimes the blade used to sever the head off was blunt, meaning that it took several blows. A peasant, on the other hand was usually hanged, this was a very painful way to die, as sometimes the initial jolt wouldn't snap the neck.
