The menu is set, the rehearsals are underway and the trumpets are polished for the event of the year—all the behind-the-scenes details as the couple gets ready to say ‘i do’.

Capt. Thomas Mountain has been perfecting the Household Cavalry’s royal salute in anticipation of performing on the steps of St. George’s Chapel when Prince Harry and Meghan Markle emerge as husband and wife. “We punch our sword out to the right, bring it all the way across until it is back in front of our face, and then lower it,” says Mountain, 28, who will rise at 5 a.m. to prep himself. “It’s going to be immense, phenomenal.” Meghan, 36, has been meeting with her bridal party and designers in London, while Harry, 33, is “exceptionally happy, extremely excited” about the upcoming day, says a friend. He’s not alone. Says Mountain: “The sense of drama is building. It’s palpable.”

The Dress

Among the top designers Meghan could have chosen for the job are Roland Mouret (who issued a “no comment” when asked in February), her frequent go-to Erdem, Ralph & Russo (who designed her sexy engagement-shoot dress), heritage British label Burberry or her pal Misha Nonoo. In royal tradition she’ll include a sprig of myrtle in her bouquet—later to be placed on the Grave of the Unknown Warrior at Westminster Abbey.

The Church

With the last American king, George III, buried beneath them in the vault, Meghan and Harry will pace about 110 steps from the altar to the grand door of the historic St. George’s Chapel on the grounds of Windsor Castle.

TheMaid of Honor Contenders

Jessica Mulroney, Meghan’s Toronto-based best pal and unofficial stylist, recently jetted to London for last-minute bridal fittings. Others who may have been tapped for the honor include Meghan’s school friend Lindsay Roth, New York-based designer Misha Nonoo and L.A.-based brand curator Benita Litt. Long shot: royal sister-in-law Princess Kate.

The Page Boy & Flower Girl

Prince George, 4, and Princess Charlotte, 3, will likely join the bridal party—as they did for Aunt Pippa’s wedding last May.

The Glam Squad

Facialist Nichola Joss will ensure Meghan’s skin is glowing. Beautician Sherrille Riley is set for eyebrow and manicure duty, and Miguel Martin Perez has been tipped as hairstylist. Joss says, “She has a fantastic face shape and looks after herself well.”

The BestMan

As expected, Prince William, 35, was officially handed the honor on April 26. William—who called upon Harry as his own best man seven years earlier— teased ahead of his toast: “Revenge is sweet.”

The Cellist

Thebride-tobe personally surprised Royal Academy of Music student Sheku Kanneh-Mason, 19.“I was bowled over when Ms. Markle called me to ask if I would play,” says the cellist, who was first spotted by Harry at a charity event. “I can’t wait!”

The Parents

Harry’s dad, Prince Charles, and stepmom, Camilla, Duchess of Cornwall, will attend alongside Meghan’s parents, Doria Ragland and Thomas Markle. Princess Diana (with Harry in 1987) will be subtly honored with white flowers, her favorite.

The Trumpet Maker

State trumpeters will herald the wedding on instruments crafted in a converted cow shed by Richard Smith, 73, of Smith-Watkins. “They’ve got to raise it up to their lips and start playing immediately,” he says. “They’ve got to get it right first time. It’s the hardest musical job in the world.”

The Honeymoon

The couple have visited Africa together twice already—and a source says they are headed to Namibia for their honeymoon. (They reportedly have a reservation at the Hoanib Valley Camp.) During their first trip there, “we camped out with each other under the stars . . . which was absolutely fantastic,” Harry said in November.

Special Guests of Honor

Invitations were sent to charity standouts like 15-year-old Diana Award winner Faith Dickinson, along with 1,200 others who have made a difference. Amelia Thompson, 12, was among the crowd at the Ariana Grande concert in Manchester last May, where a suicide bomber killed 22 people. She and Sharon Goodman—whose granddaughter Olivia Campbell-Hardy, 15, was killed—are taking a “pillar candle with all the names of the 22 victims on it,” says Thompson. “It’ll mean all the 22 people will be there.”