The Queen's official birthday salute will be subject to social distancing rules and closed to spectators - with Trooping the Colour scrapped.
Buckingham Palace has released details of the Windsor Castle event that will see Her Majesty take two royal salutes from the Welsh Guards on Saturday.
The head of state was last seen at a major event on March 9 when she attended the Westminster Abbey Commonwealth Day service with senior members of the monarchy and the Duke and Duchess of Sussex, who made their final appearance as working royals.
Saturday's ceremony will be carried out by a detachment from the 1st Battalion Welsh Guards, whose colour - or military flag - was due to be trooped this year at the Queen's Birthday Parade on Horse Guards in Whitehall.
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Stationed at Windsor Castle, the servicemen have played a key role in the military response to the Covid-19 pandemic over the past few months.
When the Queen arrives at the castle's quadrangle she will receive a royal salute which will be followed by a set of military drills and a musical performance by a Band of the Household Division.
The drills will include the colour being paraded in front of the servicemen and the ceremony will end with a second royal salute followed by the Guardsmen and the military musicians marching from the quadrangle.
The ceremony is expected to last about 20 minutes and will see the Guardsmen performing their drills two metres apart with the military musicians also observing social distancing.
Broadcaster Huw Edwards will host a BBC One programme covering the event which replaces Trooping the Colour, the national celebration of the Queen's official birthday which traditionally is staged every year in June.
It famously features a gathering of the royal family on Buckingham Palace's balcony to acknowledge the crowds in The Mall and watch a flypast.
Trooping also attracts thousands of spectators, friends and family of the soldiers taking part in the military spectacle, who fill stands around Horse Guards Parade in Whitehall where the event is normally staged.
A few days after lockdown was announced Buckingham Palace said in line with Government advice Trooping the Colour would "not go ahead in its traditional form" and a number of options were being considered.
