Britain's royal line of succession: Who is next in line to the throne?

TAMPA, Fla. (WFLA) — Britain's Queen Elizabeth II remains under round-the-clock medical supervision at her castle in Balmoral, Scotland, Buckingham Palace said in a statement Thursday.

According to reports, doctors are  “concerned for Her Majesty’s health," and members of the royal family, including the Queen's son, Prince Charles, his wife Camilla and the Queen's grandson, Prince William, are on their way to Scotland.

With more than 70 years on the throne, most alive today will have only seen the queen as Britain's monarch, but who is next in line?

Prince Charles will become king if the queen gives up her throne, retires or dies. Next in line after him is his eldest son, Prince William, Duke of Cambridge. Prince George is third in line to the throne, after his father and grandfather.

The royals have made a number of changes to succession rules over the years, making it difficult to keep track of whose next in line.

Up until Duchess Kate's pregnancy, the crown was passed from monarch to eldest son. Since King George VI had no son, his eldest daughter, Elizabeth, became queen.

What does the queen like with tea? Jam sandwiches every day

But the Succession to the Crown Act was created in 2013, before Prince George was born, to make succession to the throne based on birth order, not gender.

Now, Princess Charlotte will be fourth in line to the throne, and Prince Louis will be fifth. William’s younger brother, Prince Harry, is sixth in line, and his son, Archie Harrison Mountbatten-Windsor, will be seventh with his little sister, Lilibet right behind him.

A number of others are in line to claim the throne. Here are the top 25 in the line of succession:

1. Charles, Prince of Wales – married to Camilla, Duchess of Cornwall
2. Prince William, Duke of Cambridge – married to Kate, Duchess of Cambridge
3. Prince George of Cambridge
4. Princess Charlotte of Cambridge
5. Prince Louis of Cambridge
6. Prince Henry, Duke of Sussex – married to wife Meghan, Duchess of Sussex
7. Archie Harrison Mountbatten-Windsor
8. Lilibet Diana Mountbatten-Windsor
9. Prince Andrew, Duke of York – Queen Elizabeth’s second son
10. Princess Beatrice of York – Prince Andrew and Sarah, Duchess of York’s daughter
11. Sienna Elizabeth Mapelli Mozzi, Princess Beatrice's daughter
12. Princess Eugenie of York – Prince Andrew and Sarah, Duchess of York’s daughter
13. August Philip Hawke Brooksbank, Princess Eugenie's daughter
14. Prince Edward, Earl of Wessex – Queen Elizabeth’s third son
15. James, Viscount Severn – Prince Edward and Sophie, Countess of Wessex’s son
16. Lady Louis Windsor – Prince Edward and Sophie, Countess of Wessex’s daughter
17. Anne, Princess Royal – Queen Elizabeth’s daughter
18. Peter Phillips – Princess Anne’s son with Capt. Mark Phillips
19. Savannah Phillips – Peter and wife Autumn’s daughter
20. Isla Phillips – Peter and wife Autumn’s daughter
21. Zara Tindall – Zara Phillips married Mike Tindall, the eldest granddaughter of Queen Elizabeth
22. Mia Grace Tindall – Zara and Mike’s daughter
23. Lena Tindall, Zara and Mike’s daughter
24. Lucas Tindall, Zara and Mike’s daughter
25. David Armstrong-Jones, 2nd Earl of Snowden – Also known as Viscount David Linley