LONDON — Bookies are taking bets on who will be invited to one of the year's most exclusive events: Prince Harry and Meghan Markle's wedding in May. Everyone who is anyone in Britain is angling for an embossed royal ticket.

British heavyweight boxer Anthony Joshua, who is seeking to add two more world championships to the three he already owns, says he would be happy to interrupt his high-level training for a trip to Windsor Castle on May 19. The ebullient Joshua has not been shy, tweeting a picture of himself and Harry with the question "Need a best man?"

"I'm single," the 28-year-old told the BBC, expressing an interest in seeing if the elegant, raven-haired Markle's "got any sisters."

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(For the record, Anthony, she has a half sister, 53-year-old Samantha Grant, a divorced mother of three who has called Markle "a social climber.")

The actual guest list is a closely guarded secret. But that hasn't stopped speculation about who's in or who's out from becoming a national parlor game and the subject of wagers in Britain's legal betting shops.

Any bride and groom run into parental interference in their guest list, whether it's adding random cousins or forgotten neighbors. Yet Harry and his bride-to-be are enduring this phenomenon at a cosmic level due to the royal expectations that come along with being a grandson of Queen Elizabeth II.

At least Harry and Markle won't face the 3,500 guests that his parents, Prince Charles and Lady Diana Spencer, welcomed to their 1981 "wedding of the century" in St. Paul's Cathedral in London. They also avoided the warehouse-sized Westminster Abbey, where Harry's brother Prince William and Kate Middleton packed in 1,900 guests for a 2011 royal wedding extravaganza televised around the world.

Their wedding venue, the 15th-century St. George's Chapel at Windsor Castle, holds a mere 800 guests. Even so, it's going to be tough to cut that list.

The British royals' close relatives alone number over 50 -- and this time Princess Eugenie gets to bring a plus-one, fiance Jack Brooksbank. Harry also won't forget non-royals like Kate's sister, Pippa Middleton, her husband James Mathews, and brother James Middleton.

At William's wedding, 45 foreign royals from 20 countries were invited from nations as diverse as Spain, Norway, Malaysia, Thailand and Saudi Arabia. William also invited governors-general from Commonwealth countries (23 seats); foreign dignitaries (27); U.K. politicians (42); religious figures (31); senior military officers (14) and 80 workers from charities that he backs. Oh -- and don't forget the ambassadors from countries with ties to Britain.

William barely could squeeze in A-listers like David Beckham and TV adventure host Ben Fogle -- who may return for Harry's nuptials.

Britain's governing elite -- Prime Minister Theresa May, Foreign Secretary Boris Johnson and Chancellor of the Exchequer Philip Hammond -- would normally expect a Windsor invite. But with turmoil over Brexit roiling the ruling Conservative Party, perhaps the bride and groom should just wait until a week before the wedding, then invite whoever is still left standing.

The juiciest debate has been over invites for rival U.S. presidents Barack Obama and Donald Trump. Harry and Mr. Obama have obvious chemistry and have worked together promoting Harry's Invictus Games competition for wounded soldiers; Harry conducted Mr. Obama's first interview since leaving the presidency for the BBC. At the time, he said that he had not figured out his wedding guest list yet. Some British officials fear that an invite to Mr. Obama would anger Mr. Trump.

The royals could note that Mr. Obama, as U.S. president in 2011, was not invited to William's wedding. And they have a bit more leeway because Harry's wedding is not considered a state event. Markle, meanwhile, is a Hillary Clinton fan.

"We've changed our minds on this. We think Harry is in a position that he does not have to worry about the political implications of an invite," said Rupert Adams, a spokesman for the betting agency William Hill PLC. "We feel strongly that the Obamas will get an invite."

As for President Trump?

"We'd be very surprised to see him on the guest list," Adams said.

Canadian Prime Minister Justin Trudeau has a trifecta of ties to the bride and groom: He's the head of a Commonwealth country, host of Harry's latest Invictus Games and leader of the nation where Markle had been living.

On the celebrity front, Elton John, who turned his song "Candle in the Wind" into an anthem for the late Princess Diana, is considered a 1-50 lock for an invite (98 percent chance) and singer James Blunt comes in at 1-4. Singer/songwriter Ed Sheeran is also reportedly close to Harry's royal cousins and his U.K. tour doesn't start until a few days later.

The betting for wedding performer includes John, Sheeran, Coldplay, Joss Stone and Adele.

Yet A-listers could find themselves outnumbered by British military members and charity workers. Look for dress uniforms from both the Blues and Royals regiment and the Army Air Corps, because Harry served as a former Apache helicopter co-pilot in Afghanistan.

"You create significant bonds in a war zone," noted Adams.

Ahead of the noon wedding, Harry and Markle will take a carriage ride through Windsor so they can share their big day with the public, Kensington Palace said Monday. Charles, the father of the groom, will also host a private evening reception for close friends and family at an undisclosed location.

The friend who introduced them, Violet von Westenholz, will get a nod, along with Harry's buddies Thomas and Charlie van Straubenzee, Thomas Inskip and Arthur Landon.

Among the guests on Markle's side will be her mom Doria Ragland, dad Thomas, half brother Thomas Jr. and possibly Grant. Markle's friends include tennis star Serena Williams, stylist Jessica Mulroney, "Suits" star Patrick J. Adams and former "Made in Chelsea" cast member Millie Mackintosh.

Markle's ex-husband, producer Trevor Engelson, is not expected to receive an invitation.

But William Hill spokesman Adams admits that British bookies don't really have a clue about who the 36-year-old American will invite.

"The simple reality is ... we have been focusing on Harry over here," Adams said.