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Prince Andrew will be promoted to the rank of vice-admiral in the Royal Navy when he turns 55 next week.

The Duke of York's appointment was announced in the latest Royal Navy appointments in the London Gazette.

A Buckingham Palace spokesman said it had been "approved by the Queen in line with long-standing convention covering military promotions" for royals.

Pressure group Republic branded the move "offensive to our armed forces" and a "self-serving royal indulgence".

In a statement, the Royal Navy said: "Following his active service, His Royal Highness has been hugely supportive of the Royal Navy and has undertaken a vast amount of work for the service over many years.

"This promotion on the occasion of his 55th birthday recognises that contribution."

Prince Andrew joined the Royal Navy in 1979 as a Seaman Officer subspecialising as a Pilot.

After being awarded his "wings" he joined 820 Naval Air Squadron, serving aboard the aircraft carrier, HMS Invincible and served as a Sea King helicopter co-pilot during the Falklands War.

In 1999 he was made a commander and finished his active naval career, in 2001, at the Ministry of Defence, as an officer of the Diplomatic Directorate of the Naval Staff.

The navy established a policy in 2009 that means the prince is promoted in line with his peers who are still serving, to mark his continued contribution to the service.

He became a rear admiral on his 50th birthday.

Last month, Prince Andrew reiterated denials issued by Buckingham Palace after a US woman alleged that she was forced to have sex with him when she was 17.

Virginia Roberts alleges in court documents she was forced to do so by financier Jeffrey Epstein, a convicted sex offender.

Buckingham Palace has previously said the claims against the prince, who is fifth in line to the throne, are "categorically untrue" and lack "any foundation".

The Duke of York stepped down as UK trade envoy in July 2011 following controversy over his friendship with the American financier but appeared at a World Economic Forum reception in Davos, Switzerland, last month.