Earlier this year the Queen was made Commandant in Chief of the Canadian forces and she is returning the honour by inviting the Canadian Mounties to take part in the Changing of the Guard ceremony.
The invitation is part of the Queen's Diamond Jubilee celebrations and was a gesture first made by her father King George VI in 1936.
Acting as the Queen's personal bodyguards is an honour normally carried out by the Household Cavalry – distinctive for their red or blue cloaks, polished helmets and white plumes.
Today and Friday 15 men – and for the first time, women too – will take part in the Changing of the Guard.
The Lifeguard are the Sovereign's personal body guard and have had this role since the 17th century. When the Queen is in residence, the guard is made up of 15 soldiers including a Captain.