The current line of succession to the throne is Prince Charles, followed by his sons Prince William and Prince Harry.

The U.K. Parliament regulates the line of succession to the British throne, using guidelines laid out in the Bill of Rights (1689) and the Act of Settlement (1701).

In October 2011, Commonwealth leaders unanimously agreed to remove the centuries-old gender discrimination rule that favours first-born sons over older daughters in the order of succession to the throne.

The move came after British Prime Minister David Cameron sent a letter to Commonwealth leaders — including Prime Minister Stephen Harper — proposing to change British law so that a male heir no longer takes precedence over a female heir.

The changes would mean that if Prince William and Kate, the Duchess of Cambridge, "were to have a little girl [as their first child], that girl would one day be our queen," Cameron said.

The Commonwealth leaders also agreed to lift a ban on the monarch being married to a Roman Catholic.

According to the Act of Settlement, only Protestant members of the Royal Family who are descendants of Princess Sophia (1630-1714), the Electress of Hanover, a granddaughter of James I, can be considered for the throne.

The sovereign is required to take an oath to defend the Church of England and the Church of Scotland. A Roman Catholic is disqualified from succession to the throne.

There are more than 900 people in line for the British throne; the first 510 on the list are descended from Queen Victoria (1819-1901).

Rules specifying who inherits the throne, now based on the 1701 Act of Settlement, are not easy to change — particularly because they involve all 16 Commonwealth countries where Queen Elizabeth is head of state.

Harper has said the "obvious modernizations" were long overdue. He hasn't given a timeline for when legislation will come before Parliament for approval, but said he hopes it will be adopted quickly.

Line of succession
Sovereign: Elizabeth II (b.1926)
1. The Prince of Wales (b. 1948), Queen Elizabeth II's eldest son (Prince Charles)
2. Prince William of Wales (b. 1982), the Prince of Wales's elder son
3. Prince Henry of Wales (b. 1984), the Prince of Wales's younger son
4. The Duke of York (b. 1960), Queen Elizabeth II's second son (Prince Andrew)
5. Princess Beatrice of York (b. 1988), the Duke of York's elder daughter
6. Princess Eugenie of York (b. 1990), the Duke of York's younger daughter
7. The Earl of Wessex (b. 1964), Queen Elizabeth II's youngest son (Prince Edward)
8. Viscount Severn (b. 2007), the Earl of Wessex's son (James)
9. Lady Louise Windsor (b. 2003), the Earl of Wessex's daughter
10. The Princess Royal (b. 1950), Queen Elizabeth II's daughter (Princess Anne)
11. Peter Phillips (b. 1977), the Princess Royal's son
12. Savannah Phillips (b. 2010), Peter Phillips' daughter
13. Zara Phillips (b. 1981), the Princess Royal's daughter
14. Viscount Linley (b. 1961), grandson of King George VI through his daughter Princess Margaret
15. Charles Armstrong-Jones (b. 1999), Viscount Linley's son
16. Margarita Armstrong-Jones (b. 2002), Viscount Linley's daughter
17. Lady Sarah Chatto (b. 1964), granddaughter of King George VI through his daughter Princess Margaret
18. Samuel Chatto (b. 1996), son of Lady Sarah Chatto
19. Arthur Chatto (b. 1999), son of Lady Sarah Chatto
20. The Duke of Gloucester (b. 1944), grandson of King George V through his son Prince Henry, Duke of Gloucester
21. Earl of Ulster (b. 1974), son of the Duke of Gloucester
22. Lord Culloden (b. 2007), son of Earl of Ulster
23. Lady Cosima Windsor (b. 2010), daughter of Earl of Ulster
24. Lady Davina Windsor (b. 1977), elder daughter of the Duke of Gloucester
25. Senna Lewis (b. 2010), daughter of Lady Davina Windsor
26. Lady Rose Gilman (b. 1980), younger daughter of the Duke of Gloucester
27. Lyla Gilman (b. 2010), daughter of Lady Rose Gilman
28. The Duke of Kent (b. 1935), grandson of King George V through his son Prince George, Duke of Kent
29. Lady Amelia Windsor (b. 1995), daughter of George, Earl of St. Andrews
30. Lady Helen Taylor (b. 1964), daughter of the Duke of Kent
31. Columbus Taylor (b. 1994), son of Lady Helen Taylor
32. Cassius Taylor (b. 1996), son of Lady Helen Taylor
33. Eloise Taylor (b. 2003), daughter of Lady Helen Taylor
34. Estella Taylor (b. 2004), daughter of Lady Helen Taylor
35. Albert Windsor (b. 2007), son of Lord Nicholas Windsor
36. Leopold Windsor (b. 2009), son of Lord Nicholas Windsor
37. Lord Frederick Windsor (b. 1979), son of Prince Michael of Kent
38. Lady Gabriella Windsor (b. 1981), daughter of Prince Michael of Kent
39. Princess Alexandra, Lady Ogilvy (b. 1936), granddaughter of King George V through Prince George, Duke of Kent