Queen Elizabeth's private secretary Sir Christopher Geidt has resigned.

Queen Elizabeth

Queen Elizabeth

The 91-year-old monarch has employed Christopher as her private secretary for the past decade, but he has now revealed he will be leaving the position in October after her husband Prince Philip's decision to step down from royal duties means the Queen has "the full and active support" of the rest of the royal family.

Christopher - who has worked for the Queen in a number of roles since 2002 - will be replaced by Edward Young, who joined the royal household in 2004.

In a statement, Christopher said: "It has been my very great privilege to serve the Queen since the Golden Jubilee in 2002 and, especially, as her private secretary for the past decade. In that time, as throughout her reign, Her Majesty's authority has brought stability, purpose and colour to country and Commonwealth alike.

"With the Duke of Edinburgh's recent decision to draw back from public life, the Queen's own unwavering commitment as sovereign has the full and active support of the entire royal family. It is therefore with every confidence, and with Her Majesty's agreement, that I now hand over the responsibilities of the Queen's private secretary to my successor, Edward Young."

Prince Philip, 96, is set to retire on Wednesday (02.08.17) after he completes his final royal engagement at Buckingham Palace parade for the finale of the Royal Marines 1664 Global Challenge.

A palace spokeswoman said in a statement that the parade would "bring His Royal Highness's individual programme to a conclusion, although he may choose to attend certain events, alongside the Queen, from time-to-time."

It was revealed earlier this year that Prince Philip would be stepping down from his royal duties after the summer.

A statement released at the time read: "His Royal Highness The Duke of Edinburgh has decided that he will no longer carry out public engagements from the autumn of this year. In taking this decision.

"Prince Philip will attend previously scheduled engagements between now and August, both individually and accompanying The Queen. Thereafter, The Duke will not be accepting new invitations for visits and engagements.

"Although he may still choose to attend certain public events from time to time."