The Princess of Wales will make her first public appearance of the year when she takes part in the annual Trooping the Colour parade.
Catherine will be in a carriage procession with her children, as the Royal Family parades along the Mall.
She will also make an appearance on the balcony of Buckingham Palace.
The plans were revealed in a health update from the princess, who is continuing with her chemotherapy treatment.
This first step back into public life for Catherine comes on one of the biggest royal events of the year.
The King’s birthday parade, traditionally celebrated in the summer rather than on his actual birthday in November, sees a military parade and inspection, with music and pageantry.
This year, after his cancer diagnosis, the King will be in a carriage rather than on horseback during the procession and when he inspects the troops on Horse Guards Parade.
King Charles is “delighted” that the Princess of Wales will be at the ceremony, according to a Buckingham Palace spokesman.
In a personal message, the princess said she was “not out of the woods yet”, and had “good days and bad days”, but was “looking forward to attending the King’s birthday parade this weekend with my family”.
During the parade a regimental flag is “trooped” through the ranks of soldiers, with this being rotated among the five regiments of Foot Guards.
This year it will be the Irish Guards who take the lead, with some Irish music expected to be a feature of the parade and their mascot an Irish wolfhound making an appearance.
Gun salutes will be fired in nearby Green Park and when the royals are gathered on the palace balcony, there is usually a flypast thundering overhead.
Although these events have a strong focus on tradition, there are changes, such as allowing soldiers this year to have beards. This comes with the stipulation that there should be “no exaggerated colours”.
Also making a return will be three of the horses of the household cavalry which ran away and were injured during a rehearsal.
Ahead of this year’s Trooping the Colour there had been a dispute over a planned protest by anti-monarchists.
Graham Smith of the Republic group criticised the expense of the parade and said: “The feudal tradition of royal pageants needs to stop.”
The protest will go ahead but with a requirement not to use amplified sound.
