William and Kate, who are both experienced divers, took the opportunity to explore Belize's beautiful barrier reef – the second largest in the world – at South Water Caye.
In a video shared on their official social media pages and taken by photographer Matt Porteous, the royals were seen swimming underwater, giving each other the 'okay' hand signal, and admiring the local marine life. They also surfaced at the end of the short clip, turning towards each other and smiling as they breathed into their oxygen tanks.
WATCH: Prince William and Kate enjoy secret diving trip in Belize
The couple swam with nurse sharks, with one in particular swimming alongside them throughout their dive as they joined Edward Bettencourt, known as "Captain Gravy" and his daughter Narisha, to see the vital conservation work being done to preserve it. A royal source said: "They had a brilliant time, they saw nurse sharks."
In the voiceover, William, a keen conservationist, is heard saying: "It's really fantastic to see the underwater environment here in Belize and what wonderful work they've been doing to protect the coral and fish life.
"Belize's work on marine protection is world-leading, which is crucial when you're protecting the world's second largest barrier reef and in fact it's a UNESCO world heritage site. It's clear to see the Belizeans value their environment, whether it's the marine environment or the land environment.
"It's great to see their commitments go further and further. We should support them and value their efforts to protect both the marine and the land environments."
Kate scuba diving in Belize
The caption for the post also read: "Belize is home to the second largest barrier reef in the world. While the effects of climate change are evident, the Government of Belize and communities across the country deserve huge recognition for their efforts to restore this incredible marine environment - with a commitment to protect 30 per cent of it by 2030.
"On Sunday, we were lucky enough to spend time diving at South Water Caye, directly above the spectacular Belize Barrier Reef. It was a privilege to see for ourselves the world-leading ocean conservation work being done here."
The royal couple's dive took place privately after their visit to Hopkins Beach, but HELLO! understands the Belize Government had been very keen for them to see and experience the reef.
The Duke shone a light on Belize's conservation efforts
Both William and Kate are fans of diving, with the Duchess becoming a qualified diver in 2015. At the time, she successfully completed the Professional Association of Diving Instructors (PADI) Advanced Open Water Diver qualification, meaning the mother-of-three is able to dive up to a depth of 30 metres.
The Duke and Kate's family, the Middletons, regularly holiday in Mustique, where William has gone on deep dives to look for sharks. It is thought that Kate earned the qualification from a diving school in the private Caribbean island.
William, meanwhile, is a very experienced diver and took over from his father Prince Charles to become president of the British Sub-Aqua Club (BSAC) in 2014.
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