Prince William was behind the 'Fab Four' reunion at Windsor Castle with Kate Middleton, Prince Harry, and Meghan Markle

• Prince William played a key role in the "Fab Four" reunion on Saturday at Windsor Castle.
• The eldest son of King Charles invited Prince Harry and Meghan Markle for the royal walkabout.

Prince William played a critical role in the reunion between himself, Kate Middleton, Prince Harry, and Meghan Markle on Saturday.

Putting on a united front, the royal couples appeared outside of Windsor Castle to greet members of the public and view floral tributes left in honor of Queen Elizabeth II, who died aged 96 on Thursday. Both Markle and Middleton wore black dresses, while their husbands sported navy suits with black ties.

The reunion between the couples — once dubbed the "Fab Four" by the British press – came after William extended a last-minute invite to his brother and sister-in-law. A Kensington Palace spokesperson told The Times of London that William, who now holds the title of the Prince of Wales, invited the Sussexes to join him and Middleton on a royal walkabout in front of Windsor Castle.

"The Prince of Wales thought it was an important show of unity at an incredibly difficult time for the family," the spokesperson added, according to The Times.

Getting the foursome back together in public took extensive negotiations that ended up delaying their appearance at Windsor Castle by 45 minutes, the publication reported. Representatives for both couples did not immediately respond to Insider's request for comment.

There have been long-standing rumors of a rift between the Duke and Duchess of Sussex, and William and Middleton. Following Harry and Markle's "step back" from royal life in January 2020 and an explosive interview with Oprah Winfrey the following year, Insider's Mikhaila Friel reported that the couple's relationship with Harry's royal relatives still appeared fraught.

For the time being, however, the former "Fab Four" are likely to be spending more time in close proximity.

Markle and Harry, who initially traveled to the UK from the US for charity work prior to the Queen's death, are staying at their old residence, Frogmore Cottage, according to The Telegraph. It's located on the Crown's estate in Windsor, where Middleton and William recently moved to with their children.

Markle and Harry will remain in the UK until after the Queen's funeral, set to take place on September 19, a spokesperson for the couple told Today.