On 19 September, the Armed Forces served their former Commander-in-Chief Queen Elizabeth II for the final time by playing a central role in Her Majesty's state funeral.
The death of the Sovereign signalled the rise to the throne of King Charles III - a process confirmed by the Accession Council.
However, at the point of the Queen's death, the military switched to His Majesty's Armed Forces.
Watch: Military says final goodbye to Commander-in-Chief with leading role in Queen Elizabeth's funeral.
But it is not just one title set to change.
Many of the Regiments and Corps of the Army take the name of the monarch.
Some refer to generic Kings and Queens, not specifically to Queen Elizabeth II, and these regiments will not have to change their name.
But the units which specifically refer to Queen Elizabeth, such as the RAF Queen's Colour Squadron, will change to the King - so the RAF King's Colour Squadron.
These titles have already changed to recognise the new monarch, King Charles.