1. Heir Apparent - a person who is first in line of succession and cannot be displaced from inheriting.
The current Heirs Apparent are:
- Prince Charles, The Prince of Wales - The United Kingdom and Commonwealth Realms
- Crown Prince Frederik - Denmark
- Crown Prince Haakon - Norway
- Crown Princess Victoria - Sweden
- Prince Willem-Alexander, Prince of Orange - the Netherlands
- Prince Philippe, Duke of Brabant - Belgium
- Prince Alois - Liechtenstein
- Hereditary Grand Duke Guillaume - Luxembourg
- Prince Felipe, Prince of Asturias - Spain
- Crown Prince Naruhito - Japan
- Crown Prince Hussein bin Al Abdullah - Jordan
- Crown Prince Moulay Hassan - Morocco
- Crown Prince Salman bin Hamad bin Isa Al Khalifa - Bahrain
- Crown Prince Al-Muhtadee Billah - Brunei
- Crown Prince Nawaf Al-Ahmad - Kuwait
- Prince Lerotholi Seeiso - Lesotho
- Crown Prince Sultan bin Abdul Aziz - Saudi Arabia
- Crown Prince Maha Vajiralongkorn - Thailand
- Sheikh Hamdan bin Mohammed bin Rashid al Maktoum - Dubai
- Sheikh Tamim Bin Hamad Al Thani - Qatar
All of the people in this list will become Sovereigns of their respective countries, unless they predecease their Monarchs.
2. Heir Presumptive - a person who is expected to inherit, however who can be displaced in Line of the Succession by a future birth or other circumstances.
Current Heir Presumptive include:
- Caroline, Princess of Hanover is Heiress Presumptive to her brother Prince Albert of Monaco
- Prince Harry is Heir Presumptive to Prince William
- Infanta Leonor, who is Heiress Presumptive to her father Prince Felipe, The Prince of Asturias
- Jigyel Ugyen Wangchuck is Heir Presumptive to his brother Jigme Khesar Namgyal Wangchuck of Bhutan (who doesn't have a legitimate child as of now).
All the people in this list can be displaced in Line of the Succession in case of new births.
3. Prince Charles is Heir Apparent to the British Throne (and Thrones of the Commonwealth Realms) because as the first-born child and eldest son of the Sovereign, he cannot be displaced in Line of the Suceession and WILL become King, unless he predeceases his mother.
4. Queen Elizabeth was Heiress Presumptive (and never Heiress Apparent) because Britain still has Male Primogeniture, which means males have preference over females.
King George might have still had a son (however unlikely it was towards the end of his life), who would automatically be ahead of his sisters Elizabeth and Margaret in Line of the Succession.