Princess Charlotte made her official debut on the balcony of Buckingham Palace as Britain's royal family observed a Royal Air Force fly-past to mark Queen Elizabeth II's 90th birthday on Saturday (June 11).

Pictured in the arms of her mother Kate Middleton and with her three-year-old brother Prince George close by, the adorable 13-month-old was clad in a pink dress with matching shoes and bow in her hair.

It is the first time the princess - who is fourth in line for the throne - has been seen in public, prompting huge cheers from the crowd and thousands of swooning comments on social media.

The tiny tot even executed her first royal wave and was seen at one point cupping her hands on her ears as the planes roared overhead.

The Trooping the Colour parade at the royal palace, which featured nearly 1,500 uniformed officers and their men along with over 300 horses, also generated quite the buzz thanks to the queen's vivid green outfit.

The world's longest reigning monarch's unusually bold dress and hat combination in a green so bright to be almost fluorescent caught the eye of many, with some comparing it to the colour of Kermit the Frog.

According to AFP, she favours bright colours for public appearances so she can be easily seen by crowds, although they are normally in more muted shades.

She was accompanied by her husband Prince Philip, who wore a ceremonial red military uniform and bearskin hat.

Thousands were in attendance to see the spectacle.

Queen Elizabeth's actual date of birth is on April 21. But she also celebrates a second birthday each year in a royal tradition that harks back over 250 years.

The second is considered her official birthday and is usually marked in Britain on a Saturday in June.