The former First Sea Lord has apologised to “those he hurt” as he lost his rank over an affair with a subordinate.

Sir Ben Key was sacked from the Navy’s top job earlier this year after it was discovered he had had an affair with a colleague.

Last month, The Telegraph revealed that the affair was exposed after the husband of the female colleague filed a complaint.

An investigation into his behaviour has now been completed by the Ministry of Defence, and Sir Ben has had his service terminated and been stripped of his commission.

The investigation, which took two months to conclude, found that his behaviour had fallen “far short of values and standards expected of service personnel”.

Adml Sir Tony Radakin, the chief of defence staff, said: “We expect the highest standards of behaviour from our service personnel and our Civil Servants. We investigate all allegations of inappropriate behaviour and will take robust action against anyone found to have fallen short of our standards, regardless of their seniority.”

‘I am very sorry to those I have hurt’

Sir Ben, 59, said that he was grateful for the support of his wife and family. He added: “Serving as First Sea Lord has been one of the greatest privileges of my life, and I pay tribute to the dedicated and professional officers, sailors, Royal Marines and Civil Servants who make up the Royal Navy.

“I deeply regret my conduct in the spring of last year, which fell well below the standard I set for myself and that which I set for the Royal Navy. As such, I fully accept the decision of the Defence Council.

“I am very sorry to those I have hurt personally, and I apologise to everyone who serves with the Royal Navy. Finally, I am very grateful for the support of my wife, family and friends during a very difficult time.”

A source told The Telegraph that, when Sir Ben’s affair was reported to the MoD, he tried to go away “quietly”. However, an investigation was insisted on.

While Adml Sir Tony was inclined to let Sir Ben retire quietly to avoid embarrassment, Gen Dame Sharon Nesmith, the vice chief of the defence staff, and John Healey, the Defence Secretary, felt an inquiry should take place.

Sir Ben will continue to receive his pension despite his dismissal from service. It is the first time in 500 years that the head of the Royal Navy has been investigated for misconduct.