Celebrity royalty including the Clooneys, the Beckhams, Idris Elba, Elton John and Oprah Winfrey are among some of the world's biggest stars to arrive for the royal wedding today sending fans outside into a frenzy.

Prince Harry and Meghan Markle are less than 90 minutes from marrying and the groom is already on his way to Windsor Castle for potentially the most A-list wedding in history.

Outside St George's Chapel up to 100,000 fevered well-wishers gathered outside in glorious British sunshine to cheer the couple into their new married life.

Harry enjoyed his last night of single life with best man Prince William at Coworth Park, a five-star country house a stone's throw from Windsor and was swept out of its gates in a blacked-out people carrier as he went to get ready.

The 2,000-plus excited guests have largely arrived at Windsor Castle for the biggest royal wedding in Britain since Prince William married Kate in 2011 with more than 21million UK household set to watch and 23million expected to tune in from America.

St George's Chapel will soon be packed with royals including the Queen and Prince Charles, who will take Meghan to the altar in the absence of her father Thomas Markle while Harry's uncle Earl Spencer has already arrived along with all the Middletons apart from Kate.

Her mother Doria Ragland, 62, will take centre stage as will Hollywood royalty including Oprah Winfrey, Idris Elba, George Clooney and his wife Amal, tennis star Serena Williams and many of Meghan's Suits co-stars.

Princess Diana's son's whirlwind romance with the US-born actress, 36, has captured the public's imagination and they will become the Duke and Duchess of Sussex when they marry.