Wearing a pink dress with matching pink hair grip, the little princess, for the very first time, took to the balcony of Buckingham Palace to watch the Trooping the Colour ceremony with the Duke and Duchess of Cambridge, the Queen, Prince George, Prince Harry and her great-grandfather, Prince Philip.
In fact, 45 members of the royal family, along with huge crowds of the public, turned out to wish the Queen a very happy 90th birthday as three cheers rang out across The Mall.
Prince Charlotte, along with her brother George, looked absolutely delighted as the traditional flypast of historic and modern aircraft took place, although it may have been a little loud at one point, as she put one hand over an ear while being held by the mum Kate.
The royals stood and watched as military aircraft, including a Spitfire and Hurricane, soared overhead with the Red Arrows leaving a trail of red, white and blue smoke to end the impressive display.
During the Queen's celebrations Kate delighted one royal fan in particular, by revealing a glimpse into Princess Charlotte's personality - and it seems she might have a feisty toddler on her hands!
One attendee, Glynis Double, explained how Kate discussed how her kids are getting along.
'The Duchess was saying how happy she was to be here, and how lovely the service was.'
When speaking about Charlotte, who recently turned one, the Duchess told her: 'Oh, she is very cute but she has got quite a feisty side!'
Glynis added: 'I then asked her about George and she said he was a really lovely little boy. She said she hopes that George will keep Charlotte in order!'
We love the idea of big brother George keeping Charlotte in check, and the pair certainly looked very smart as their proud great-grandmother looked on. Happy Birthday your majesty!