A prince was a royal title.
On Earth, it often referred to the son of a monarch. Princes were addressed as Highness. (AUDIO: The Death of Captain Jack) However, a Prince could also act as an absolute monarch in his own right, with no King above him. (COMIC: Who's That Girl!)
The Devil was known as "the Prince of Evil" or "the Prince of Darkness." (TV: The Dæmons) One of the Beast's titles was "the Deathless Prince" or "the Prince." (TV: The Impossible Planet / The Satan Pit) The Sixth Doctor once referred to the Tremas Master as "the Prince of Darkness." (TV: The Mark of the Rani)
Princes
Hector, Paris and Troilus were princes of Troy in circa 1200 BC. (TV: The Myth Makers)
In 9th century Sudan, Prince Omar was the son of Lord Cassim. (AUDIO: The Destroyer of Delights)
The Princes in the Tower was the collective name for Edward V of England and his brother Richard who were locked up in the Tower of London. What happened to them was a mystery. (AUDIO: The Kingmaker, The Battle of the Tower, PROSE: Sometime Never...)
Prince Rupert of the Rhine was a nephew of King Charles I of England and Scotland who fought on the side of the Cavaliers during the English Civil War. (PROSE: The Roundheads)
Prince Charles Edward Stuart, better known as Bonnie Prince Charlie, was an English and Scottish prince of the Stuart dynasty and grandson of King James II and VII. During the Jacobite rising of 1745, he rebelled against King George II of Great Britain to try and take the throne, but was unsuccessful. (TV: The Highlanders)
Prince Albert was the husband of Queen Victoria of the United Kingdom. (TV: Tooth and Claw)
Prince Felix Yusupov was a Russian aristocrat in the early 20th century. He was one of the conspirators responsible for the death of Grigori Rasputin. (PROSE: The Wages of Sin)
Prince Charles was a British prince. In 1981 he married Princess Diana (TV: The Lodger, PROSE: Prisoners of the Sun) and by 2010 was married to Camilla. (TV: The Empty Planet) He eventually succeeded Queen Elizabeth II as King Charles III. (PROSE: Revenge of the Judoon)
Prince Genei was the leader of an alien invasion of Earth around the end of the 20th century. (PROSE: Useless Things)
Charlie Smith was a Rhodian prince and the last of his kind after the Rhodians were killed by the Shadow Kin. (TV: For Tonight We Might Die)
A descendant of Adelaide Brooke fell in love with a Tandonian prince. (TV: The Waters of Mars)
In the 24th century, Prince Reynart was the rightful ruler of Tara. (TV: The Androids of Tara)
By 2540 there was a Draconian prince, son of the Draconian Emperor. (TV: Frontier in Space)
In 4035, Zixlyr was an Ice Warrior prince and the ambassador to Peladon after the disappearance of his twin sister Alixlyr. (AUDIO: The Bride of Peladon)
Kylo Sorsha was a pyrokinetic prince of the Royal House of Sorsha in the Drashani Empire. (AUDIO: The Burning Prince)
Zanith was a prince. (AUDIO: Time Works)
Planet Okul's native inhabitants, the warlike time-travelling Frovians, were led by Prince Luj. (COMIC: Who's That Girl!)