She was branded moody, but today we can reveal why the Duchess of Cambridge looked out of sorts at Trooping the Colour – riding in horse-drawn carriages makes her seasick.
Kate was nauseous from the swaying of the vintage coach as she progressed up the Mall with Prince Harry, 34, Meghan Markle, 37, and the Duchess of Cornwall, 71.
And we can reveal the Duchess, who chose to go by car to her 2011 wedding, has an unlikely ally.
The Queen gets seasick too – despite sailing in the Royal Yacht Britannia for 43 years – and recommended her favourite pills to Kate.
“The truth is the Duchess of Cambridge gets very seasick and doesn’t enjoy the rocking motion of carriages,” a royal source insisted.
“Worrying she may be ill on such an important occasion as Trooping the Colour added to her stress.
“Protocol meant she had no choice but to go by state carriage.”
The Queen admitted last year her 1953 Coronation was blighted by a “horrible” two-hour journey in a 200-year-old, 24ft, four-tonne carriage pulled by eight horses.
She said it was “only sprung on leather and not very comfortable”.
Dr Qadeer Arshad, of Imperial College London, said: “Motion sickness is down to mixed messages coming from your ears and eyes.
“The most effective drug makes you drowsy so wouldn’t be suitable for royals before a state occasion.”
But he promised help for them soon: “We’ve developed a technique using electricity to stimulate parts of the brain to ease symptoms.”
Buckingham Palace was “unable to comment” on Kate’s seasickness.