Kate Middleton crowned deep sea diving expert

The Duchess of Cambridge has gained her advanced diving qualification. Pool Photo / Fiona Goodall

They have confessed to being "very competitive" when it comes to sports including tennis, skiing and sailing.

The Duke and Duchess of Cambridge can add scuba diving to the list - as Kate has now equalled William's level by gaining an advanced qualification.

It means Kate is qualified to dive to a depth of 30 metres and will be able to keep up with her husband on shark dives in the Caribbean.

William last year became the third generation of the monarchy, after his father and grandfather, to head the British Sub-Aqua Club (BSAC) - the sport's governing body. He has said he hopes Prince George and Princess Charlotte will take an interest in diving.

It is believed Kate secured the advanced open water qualification at a diving school in Mustique in the Caribbean, a favourite holiday destination of the Middleton family.

Kensington Palace confirmed she had achieved the credential. A spokesman said: "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."

The advanced qualification involves completing five dives - including deep and underwater navigation dives.

Those who take the course also learn how to plan dives and deal with the physiological effects and challenges of deep water.

They are taught how to explore ship wrecks, identify fish and take pictures underwater. Advanced divers need to carry equipment including a compass and a knife to be used in emergencies, such as becoming caught up in fishing nets.

The duke and duchess have admitted to a healthy rivalry, and it has often been evident during sporting challenges on official engagements.

Before the couple went head to head in a dragon boat race in Canada in 2011, the duke said: "We are both very competitive. She beats me at tennis and skiing but I am better at the rest."

William won that event but his wife got revenge last year, beating him in a race of America's Cup yachts in New Zealand.

Kelly Fisher Katz, who met the couple in Mustique while on holiday with her husband Martin, told The Sunday Telegraph: "We went diving and they went very deep, more than 90ft. Our instructor said Martin and I weren't qualified to go on the shark dives that they went on. They're quite the sportsmen."

Eugene Farrell, BSAC chairman, said: "We are thrilled that the Duchess of Cambridge shares her husband's interest in the underwater world."

- Daily Mail