Catherine joins William qualifying as an advanced scuba diver

While it was common knowledge Catherine enjoyed sailing as a sport, her involvement with diving has been kept secret until now.

The qualification is the most advanced taken by most recreational divers; wanting to dive deeper than this carries risks, such as nitrogen narcosis, a sensation similar to drunkenness, giving the diver less control over themselves – clearly dangerous underwater.

The Duke has been diving for years, something no doubt encouraged by his father. Last year, he took over as president of the British Sub-Aqua Club from Prince Charles, and said that he would love for Prince George to take up the sport later in life.

To earn the qualification, divers must complete five dives, including a deep dive and an underwater navigation dive. On these submersions, they are taught how to cope with the physical effects of the depths, such as nitrogen build-up.

Three other options can then be chosen, including photography, buoyancy control, fish identification, night time diving and exploring wrecks; the mother-of-two is also a keen photographer, having taken these pictures of her children recently, and so we expect this to have been one of her choices.

William and Catherine enjoy regular holidays to the island of Mustique in the Caribbean, whose waters are chosen by many for diving. The Duchess can now join her husband at the same depth with her newly acquired skills.