The former head of the Royal Navy Admiral Sir Ben Key has been sacked following an investigation.
Sir Ben stepped back from his role as First Sea Lord in May after an investigation was launched into an alleged relationship with a female colleague, a person familiar with the matter told Sky News at the time.
A full investigation has resulted in the termination of his service and commission, the Ministry of Defence said.
In a statement today, Chief of Defence Staff Admiral Sir Tony Radakin 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."
In a statement after his sacking was announced, Sir Ben Key said: "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."
He was First Sea Lord from 2021 until May this year, when he was succeeded by General Sir Gwyn Jenkins of the Royal Marines.
Educated at Bromsgrove School, in Worcestershire, Admiral Sir Ben joined the navy in 1984 as a university cadet.
He qualified as both helicopter aircrew and as a principal warfare officer and as a junior officer saw service around the world in a variety of frigates and destroyers.
He was made a Commander of the British Empire (CBE) in 2016 and a Knight Commander of the Order of the Bath (KCB) in 2021.