Royal Wedding 2018: Harry and Meghan's guests arrive in London ahead of big day

Friends and family of Meghan Markle and Prince Harry have begun arriving in London for the Royal Wedding.

The nuptials will take place at Windsor Castle on Saturday, with many guests choosing to arrive early to take in the sights of London.

Meghan's Suits co-star Gabriel Macht and his wife Jacinda Barrett are among the attendees hitting the town and sharing their tourist snaps along the way.

Jacinda, an Australian actress and former model, shared a photo on Instagram of her and her daughter Luca kissing outside Buckingham Palace.

She also posted a photo sightseeing with Gabriel.

Another of Meghan's Suits co-stars, Sarah Rafferty, is in Europe – posting photos of her family in Paris.

It's expected she'll head to London in the coming days.

A number of celebrities are rumoured to be attending, including all five members of the Spice Girls, Ed Sheeran, Sir Elton John and Serena Williams.

Meghan's friend, actress Priyanka Chopra, confirmed she received an invitation telling US Weekly in April she was attending – but didn't know what to wear.

RELATED: Meghan Markle's mum Doria seen heading to LAX ahead of royal wedding

Harry and Meghan will marry at St George's Chapel in the grounds of Windsor Castle in front of a very select crowd.

They will have two receptions, the first to take place inside St George's Hall immediately after their carriage procession through Windsor.

It'll be a formal affair for 600 guests and is hosted by Her Majesty the Queen.

The hall is rather small – just 55 metres in length – and is traditionally used for State banquets.

The second reception takes place in the evening at Frogmore House, with Prince Charles hosting the event.

RELATED: Prince Charles and Camilla fly into Kensington Palace for the royal wedding

Just 200 people are invited and it is strictly for close friends and family of the couple.

9Honey royal commentator Victoria Arbiter says an invitation to party into the night Harry and Meghan is something money cannot buy.

"It's a much-coveted invitation to the evening reception, this is for very close family and friends so you know you are the tight, inner circle if you are going to Frogmore in the evening," Ms Arbiter says.

"William and Harry both have incredibly loyal friends, and they like to surround themselves with that group and they're so loyal in the sense that they don't talk at all to the media."

From the moment Harry and Meghan announced their engagement, they've been doing things their own way.

"In the Charles and Diana days it was the war of the words played out in the newspapers via the couple's friends, so it's lovely to see that Harry and William, and by extension Meghan and Kate, are surrounded by such a tight group of friends."

It's highly likely Meghan's acting friends will be attending the evening reception.

Harry's friend from his Eton school days, Tom Inskip, is expected to make the cut. Harry was rumoured to be best man at his Jamaican wedding last year, soon after Harry and Meghan started dating. Meghan and Harry were photographed at the event, on the beach.

Frogmore House is one kilometre from Windsor Castle, so will offer Harry and Meghan some privacy from the masses.

It was the location for their official engagement photos in November.

The spacious property has been a Royal Residence since 1792 and its garden house the mausoleum of another, very famous royal love story, Queen Victoria and Prince Albert.

Watch Harry & Meghan, The Royal Wedding Saturday May 19 from 7pm on Nine, nine.com.au and 9Now

RELATED VIDEO: Royal expert Victoria Arbiter responds to the Royal Wedding drama.