As explained by one royal expert, any desired changes are first to be discussed and voted by MPs in the House of Commons.
Royal historian Marlene Koenig told Royal Central: "Succession to the throne is based on legislation including the Succession to the Crown Act, which includes the Act of Settlement.
"It would take an act of Parliament to remove a person from the line of succession.
"Edward VIII could not abdicate without an act of Parliament.
"When the first Duke of Sussex (Prince Augustus, George III's son) and the Duke of Cambridge (Prince George, son of Prince Adolphus) married women in contravention of the Royal Marriages Act, they did not lose their rights, but their wives and children could not their rank and children did not have dynastic rights to the throne and sons could not inherit the peerage."
Former King Edward VIII was allowed to step down as monarch to head to Paris and marry US socialite Wallis Simpson only after Parliament voted in favour of this move in December 1936.
Another member of the Royal Family who has stepped back from royal duties but remains in the line of succession is Prince Andrew.
The Duke of York is currently eight-in-line to the throne, despite having announced in mid-November he would temporarily stop to carry out royal engagements following his car crash interview with Newsnight's Emily Maitlis.
Prince Harry and Meghan have also renounced to the use of their full titles with the HRH styles.
However, they will retain them for the time being, as the Queen can strip someone of their styles only if she issues a Letters Patent.
A similar move would partially modify the decree issued by King George V in 1917, which states who should receive the HRH styles and royal titles.
The last time the monarch issued new Letters Patent was December 2012.
With her move, the Queen declared that all of the Duke and Duchess of Cambridge's children will have the title of Royal Highness and be styled Princes and Princesses.
The document read: "The Queen has been pleased by Letters Patent under the Great Seal of the Realm dated 31 December 2012 to declare that all the children of the eldest son of The Prince of Wales should have and enjoy the style, title and attribute of Royal Highness with the titular dignity of Prince or Princess prefixed to their Christian names or with such other titles of honour."
Prince Harry and Meghan have started today a new chapter of their lives as minor royals. The couple has officially stepped down as senior royals on March 31, and from today Meghan and Harry are no longer allowed to carry out royal engagements, use their His/Her Royal Highness styles and use the word 'royal' as part of their brand name.
However, Meghan and Harry are retaining their full titles and the Duke of Sussex remains sixth-in-line to the throne.
Similarly, his son Archie Harrison Mountbatten Windsor, who was not given a royal title upon birth, remains seventh-in-line to the throne.
Now Express.co.uk is asking its readers whether they think Prince Harry should be removed as heir.
Removing an heir from the line of succession isn't a matter that can be dealt with by the sovereign.
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