Names on the star-studded guest list include Prince William and Kate Middleton, Prince Harry, Princesses Beatrice and Eugenie and Harry's long-term girlfriend Cressida Bonas.
Nightclub owner Guy has been friends with William and Harry for years, and has reportedly asked the brothers to act as ushers at his wedding.
Prince William, Prince Harry and the Duchess of Cambridge
The ceremony will take place in Memphis, Tennessee — as the groom's fiancée Lizzy is American —on 3 May 2014. The celebration will carry on into a three-day party.
Guy denies he is Prince George's godfather
Apart from Prince Harry, Guy will be one of the last members of the royal brothers' inner circle of friends to tie the knot. He attended the royal wedding of Prince William and Kate in April 2011, and while Harry was Best Man, it was party-lover Guy who was tasked with arranging William's stag do.
Engaged couple Guy Pelly and Lizzy Wilson
In the past, Guy has been labelled as a "party animal" who is often seen enjoying nights out with the princes in London's Mahiki, Whisky Mist and Tonteria — celebrity hotspots that he has opened and managed.
The London aristocrat, whose mother Lady Carolyn Herbert was close friends with the late Princess Diana, has always remained fiercely loyal to the princes and rarely speaks about them in public.
Cressida Bonas and Prince Harry
Royal watchers will be keen to note whether Cressida's attendance to the wedding will be a sign that she and Prince Harry could be walking down the aisle soon. The young couple have been growing more and more serious about each other and have been spotted at high-profile events together.
Cressida's makeup free selfie for Cancer Research UK
Just last month, the 25-year-old dancer moved to Shepherd's Bush in west London, just a few tube stops away from Prince Harry's royal residence.
Friends of the pretty blonde have said that while there is speculation that the royal could propose soon, Cressida "has no intention of living with Harry just yet, despite what people have been saying."