Prince George and Princess Charlotte have given their fans quite a few adorable pictures with their appearances on the balcony of Buckingham Palace on the annual occasion of Trooping the Colour - celebration of their great-grandmother Queen Elizabeth II's official birthday.

However, the eldest children of Prince William and Kate Middleton are likely to miss their balcony appearance later this week, as well as a significant royal milestone they were expected to mark at this year's celebration. While Queen Elizabeth II's official birthday is celebrated on the second Saturday of June with much fervour every year, the annual military parade at the Buckingham Palace will be replaced by a mini version this year to follow social distancing measures amid coronavirus pandemic.

A much more scaled-back version of Trooping the Colour will be held at Windsor Castle, where the queen has been isolating with husband Prince Philip since the outbreak of COVID-19 in March. Kensington Palace, the official residence of the Cambridges, hasn't confirmed if Prince William, Kate Middleton, and their three children will attend the celebrations at Windsor Castle on Saturday, June 13, reports Hello.

Prince George, six, and Princess Charlotte, five, were expected to make their debut in the carriage procession at this year's Trooping the Colour. The British monarch and her family usually take part in the royal procession, travelling from Buckingham Palace to Horse Guards Parade, where the monarch takes the salute and the inspection. The carriages then return to Buckingham Palace via The Mall, where the family gathers on the balcony to watch the fly-past.

The royal siblings' procession debut was expected last year as well, when George was five and Charlotte was four, as their father Prince William and uncle Prince Harry had also made their debuts prior to their fifth birthdays. George and Charlotte were likely to join a carriage with their mother Kate Middleton, just like William and Harry did with their mum Princess Diana and the Queen Mother.

Princess Charlotte and Prince George
Princess Charlotte of Cambridge, Prince George of Cambridge look out from the balcony of Buckingham Palace during the Trooping the Colour parade on June 17, 2017 in London, England. Getty

However, Kate instead shared a carriage with brother-in-law Prince Harry and sister-in-law Meghan Markle, who was making her first appearance since the birth of her first child Archie. Last year's parade also marked the first balcony appearance of George and Charlotte's younger brother Prince Louis.