The beautiful bride switched from her stunning elegant, formal pure white wedding gown by Clare Waight Keller for Givenchy, to a glamorous lily white halter neck by Stella McCartney for the black-tie evening do.
The US star – now a duchess and an HRH – is giving a speech at the party, which is being hosted by her father-in-law the Prince of Wales.
Harry drove his new wife from Windsor Castle in a silver-blue classic convertible Jaguar E-Type Concept Zero which was originally manufactured in 1968 and has been converted to electric power.
The happy couple waved and smiled as they headed to meet their friends at the celebration, which stretched into the early hours.
Meghan wore shoes from Aquazurra made in silky satin, with nude mesh, with soles painted in baby blue.
Her hair – in a relaxed up to do – was styled for the reception by George Northwood.
The car’s number plate bore the date of the wedding – E190518.
Guests were able to rest and change before the start of the evening celebrations following the lunchtime reception in the castle’s medieval St George’s Hall hosted by the Queen.
Comedian James Corden acted as a compère for the evening, it was reported.
Following a ceremony which broke with tradition, Meghan was expected to stamp her own imprint on the evening celebration by giving a speech of her own.
The couple were then expected to let their hair down and enjoy their first dance as husband and wife.
The closest friends of the newlyweds will be among those in attendance including Canadian stylist Jessica Mulroney and other confidantes such as Benita Litt and designer Misha Nonoo.
Serena Williams pulled out all the stops as she dazzled with her second outfit – a luxury designer frock.
The tennis champion had already stolen the show during the wedding ceremony in a nude pink asymmetric neckline gown.
And she did it all again after taking a quick nap with baby daughter Alexis Olympia ahead of tonight’s knees-up.
Sharing snaps of the dramatic Maison Valentino gown on Instagram, Serena thanked creative director Pierpaolo Piccioli for “making me look special on this special evening”.
The 17th-century royal residence stands about half a mile south of Windsor Castle in Windsor Home Park.
It offers the new Duke and Duchess of Sussex the privacy to celebrate their marriage away from the cameras.
The name Frogmore is derived from the frogs which have always lived in the low lying marshy area.
It was built in around 1680 by Charles II’s architect and in 1923, the Queen’s parents – the future George VI and Queen Elizabeth – spent part of their honeymoon there.
It is only open for people to view on three ticketed charity open days a year, as well to pre-booked groups in August.