Also in attendance was Harry's new wife, Meghan Markle.
The source said: 'The possibility of a reunion has been discussed and Meghan looks set to incorporate it into her trip.
See more of her look here.
In the wake of the royal wedding, Meghan's father has done interview after interview about her, making one wild claim after another, including that she is "terrified" of her new life and that Princess Diana would have "loathed" the way she is treating him.
Due to Mustique's private status and strict security, happy snaps from their vacations are basically non-existent but locals and other guests are happy to confirm the Duchess and Prince William's regular appearances on this tropical island idyll.More news: Trump Thanks Kim for Repatriating Remains of Fallen US Soldiers
Harry, who was star of the show just weeks ago, stayed low-key in morning dress and sunglasses as he accompanied Charlie van Straubenzee into St Mary the Virgin Church in Frensham, Surrey.
While Meghan uses Haz, Prince Harry's friends call him Potter or Spike.
The Duke and Duchess of Cambridge have been regularly holidaying here since 2008, usually with Middleton's side of the family, and their most recent visit is no exception with Grandpa and Grandma Middleton accompanying the Cambridge family on their summer vacation, their first as a family of five.
This discovery was made during an Invictus Games reception in London, when Prince Harry was heard calling out the name Meg several times before Meghan turned around. I used to have a phone number and text messages for her personal aides at the Palace, but after I said a few critical words about the Royal Family changing Meghan, they cut me off'.
OK so Cruella de Vil is retreating LOL let me know how that works out for you.