Donning a navy dress and coat, Meghan delighted fans as she waved and smiled gracefully while her son Archie remained tucked away in Windsor.
Meanwhile, the Duchess of Cambridge looked absolutely glowing in a pale yellow ensemble for the special event which celebrates the Queen's birthday.
The Queen's official birthday is actually on 21 April.
The different day was actually picked all the way back in 17th century by Governor Arthur Phillip declared a holiday to mark the birthday of the King (or her Majesty the Queen) of Great Britain.
The day kicked off in London's St James's Park, with the Queen's birthday parade and the horse guards parade (the royal horse artillery).
Astute fans will note Prince Andrew (the Duke of York), HRH Prince Charles (the Prince of Wales) and Princess Anne all join in royal salute for the birthday celebration, by doing a march past crowds through to the palace.
But fans all hold out to see members of the royal family all join the Queen to watch the flypast by the royal air force.
The stunning pageantry - which is broadcast live across the globe - always gets her Majesty to crack a smile.
This year it is expected Prince George and Princess Charlotte will have their little brother one-year-old Prince Louis join them for the first time on the balcony of Buckingham Palace to view the colour parade.
One of the best things about the day are the stunning outfits. The royal dress code means their finest threads and definitely no denim jeans.
WATCH: Meghan and Harry celebrate first wedding anniversary