The Queen has officially invested the Duke of Edinburgh with the Insignia of a Knight of the Order of Australia at Windsor Castle.

The investiture took place in the White Drawing Room in Windsor Castle, where both The Queen and The Duke of Edinburgh are currently in residence, at midday on Wednesday, London time.

"You're still a knight down there in the colonies, dear." Credit:Getty Images

Australia's London High Commissioner Alexander Downer was present for the ceremony but declined through a spokesperson to comment on the occasion.

A Buckingham Palace spokesperson told Fairfax the conversation between the Queen and her husband during the ceremony would not be made public. It is standard practice during royal audiences for no details to be given about what was said.