The Queen's Platinum Jubilee: Kate Middleton gives update on Queen's health

The Duchess of Cambridge is said to have revealed the Queen is "fine" despite suffering "discomfort" during the first day of her Platinum Jubilee celebrations.

Kate Middleton, reportedly spoke to a guest at a jubilee event yesterday where she revealed that Her Majesty found Thursday's events "very tiring".

Queen Elizabeth II was seen beaming as she joined her family on the balcony of Buckingham Palace on Thursday afternoon in front of tens of thousands of cheering fans to watch a 70-strong aircraft RAF flyover.

Hours later, Buckingham Palace officials said the Queen would not be attending the service of thanksgiving for her 70-year reign as she had experienced some "discomfort" during the ceremony.

At a reception at London's Guildhall on Friday, the Duchess is said to have told an attendee the Queen had found the day "very tiring".

Gill Smallwood, who lives in Bolton and runs domestic violence charity Fortalice, had asked how Her Majesty was faring.

She said: "Kate said, 'Yes, she was fine, it was just very tiring yesterday, and she had had a lovely, lovely time'."

Queen Elizabeth was all smiles at the Trooping the Colour ceremony on Thursday but the same can't be said for Prince Louis. Photo / Getty Images

The Duchess also told Ms Smallwood that her children, Prince George, eight, Princess Charlotte, seven, and Prince Louis, four, and also "had a lovely time" on Thursday.

All three children appeared on the balcony alongside their great-grandmother for the first day of her four-day Platinum Jubilee celebrations.

Buckingham Palace aides said she made the decision to stay home on Friday with "great reluctance".

They said she felt unable to attend after considering the "journey and activity required to participate" in the service at St Paul's.

Despite saying she was pulling out of Friday's thanksgiving service, the Queen smiled for the nation as she lit the first of a chain of more than 3,000 beacons across the UK and Commonwealth in the grounds of Windsor Castle.

It is not yet known if the monarch will make another public appearance at the Jubilee celebrations, which will include a pageant on Monday NZT and a concert on Saturday.