Why Harry's beard poses a problem
Prince Harry is unlikely to be wearing his Household Cavalry uniform to his wedding - unless he shaves off his beard, one historian has predicted.
Hugo Vickers said the Army does not permit beards - although Harry has previously appeared in his Blues and Royals uniform sporting facial hair.
"He's not able to wear his Royal Horse Guards uniform with a beard," Mr Vickers said.
"He does it sometimes but they don't like it. That's why when he took the parade at Sandhurst, he wore a suit."
In December, the prince wore a dark suit and overcoat, with medals on the outside, when he represented the Queen and inspected graduating officer cadets at the Sovereign's Parade at the Royal Military Academy Sandhurst in Camberley, Surrey.
British Army rules do not allow beards, except in rare circumstances, such as because of skin complaints, or for religious reasons.
Pioneer Sergeants are the only rank allowed to have a beard, although members of the Special Forces can when behind enemy lines.
Harry is, however, no longer a serving officer and therefore military rules may not apply to him.
He trained at Sandhurst, served in Afghanistan and became a Captain in the Household Cavalry's Blues and Royals (previously known as the Royal Horse Guards and the Royal Dragoons).
Harry left the forces in June 2015 and was first spotted with a beard in September the same year.
Four years earlier, he wore a Blues and Royals uniform to the Duke and Duchess of Cambridge's wedding when he was clean shaven.
He had a beard when he wore a military dress coat at the Cenotaph last November, which prompted criticism from some quarters.
It is thought Harry will wear his uniform of the Captain General of the Royal Marines to his wedding.
He recently took over the role from the Duke of Edinburgh after his grandfather's retirement.
The Royal Marines is the UK's elite amphibious fighting force and is part of the Royal Navy, which has always allowed full beards as long as permission is granted.
Christopher Gale, senior curator of The National Museum of the Royal Navy in Portsmouth, explained what Harry's dark blue Royal Marines uniform would look like on his wedding day should he select it.
His trousers would feature a red stripe down the side and he would wear a crimson and gold sash around his waist, and his hat would be a peaked cap with a white crown and red band.
Mr Gale told the Press Association: "For formal occasions, the Captain General would normally wear the uniform of a Royal Marines General Officer.
"This would predominantly follow the Army pattern uniform including the dark blue tunic, dark blue trousers with a wide red stripe down the leg and a crimson and gold waist sash."
"Particular differences for the Royal Marines General Officer include the tunic buttons and the Royal Marines pattern peaked cap with a white crown and red band.
"However, the cap badge would be of the Army General Officer's type, rather than a Globe and Laurel.
"The rank badges on the shoulders of the uniform would be the rank of a Field Marshal."
The rank of Captain General - the ceremonial head of the Royal Marines - stems from 1882 when Prince Alfred, the Duke of Edinburgh, was made Honorary Colonel of the Royal Marines.
The title was changed to Colonel-in-Chief when the Duke of Cornwall and York, later King George V, was appointed in 1901.
George VI then changed the title to Captain General in 1948, and the Duke of Edinburgh was appointed to the role after Elizabeth II's coronation.