Kate Middleton, the Duchess of Cambridge, is now an advanced scuba diver after having successfully gained her open water certification in Mustique.

The Telegraph reports that Kensington Palace has confirmed that the Duchess has passed a Professional Association of Diving Instructors (PADI) Advanced Open Water Diver qualification, meaning she can dive to a depth of 30 metres (98 feet).

It is the most advanced qualification held by most recreational divers, since venturing deeper involves risks such as nitrogen narcosis, a sensation similar to drunkenness, sometimes referred to as “rapture of the deep.”

Divers can only stay at a depth of 30 metres for a maximum of 20 minutes if it is their first dive of the day, or for much shorter periods if they have done other dives.

On the way back to the surface, they have to stop for three minutes at a depth of 5 metres to allow for the body to expel nitrogen that has built up at depth.

Compulsory equipment includes a dive knife, which may be used in emergencies such as becoming entangled in fishing nets, and a compass.

To pass the PADI advanced qualification, divers must complete five dives, including a deep dive and an underwater navigation dive, during which they are taught how to cope with the physiological effects of deeper scuba diving.

The other three dives are chosen from a range of options including photography, buoyancy control, fish identification, night time diving and wreck exploration.

The advanced qualification has enabled the Duchess to join her husband, Prince William, on deep dives to look for sharks during breaks at the Middleton family’s holiday haunt in Mustique.

Prince William has been diving for much of his life, encouraged by his father the Prince of Wales, whom he succeeded last year as president of the British Sub-Aqua Club (BSAC).

A spokesman for the Duchess told The Telegraph: “Diving is something the Duchess very much enjoys, and the Duke of Cambridge, who is of course President of the BSAC, has said in the past that he is hopeful his children will become interested in the sport.”

Eugene Farrell, chairman of the British Sub-Aqua Club, commented: “We are thrilled that The Duchess of Cambridge shares her husband’s interest in the underwater world and has further progressed her diver training.

“Last summer while diving with BSAC, The Duke of Cambridge suggested [Prince] George may also one day follow in his footsteps, so we hope in the future the whole family may share the same passion for scuba diving.”

The Duke and Duchess of Cambridge are known for their competitive nature when it comes to sport.