Royal Marine Alexander Blackman has spoken of his "profound sense of relief" after his sentence for shooting dead an injured Taliban fighter in Afghanistan was reduced.

The commando, who has spent more than three years in jail since being convicted of murdering the insurgent, also paid tribute to his wife for providing support he said "simply sustained me".

Following an appeal, judges sentenced Blackman to seven years for diminished responsibility manslaughter, meaning that because of time already served he could be freed next month.

He told the Daily Mail he had been "braced for the worst" during the hearing at the Court Martial Appeal Court in London on Tuesday.

He said: "My heart sank when the judge started talking about my current sentence being the equivalent of 16 years, and I thought it was somehow leading to a larger sentence.

"I just felt a profound sense of relief when they said seven."

Claire Blackman said she was "overjoyed" at the outcome, having tirelessly campaigned for her husband's release.

She said: "This is the moment that we have all been fighting hard for. It is hard to believe that this day is finally here."

Blackman said he is "an extremely lucky man to have Claire as a wife".

He added: "We hear so many other stories of relationships going bad when you are inside. That hasn't happened for us. Her love and support has simply sustained me."

A panel of five judges, headed by Lord Chief Justice Lord Thomas, sentenced Blackman, 42, from Taunton in Somerset, to the term of seven years following the recent quashing of his murder conviction for the 2011 killing.

Announcing the decision, Lord Thomas said: "As with any person sentenced to a determinate term, his release will ordinarily be at the halfway point of the sentence."

Blackman, who watched Tuesday's proceedings by video link, has already spent almost three and a half years in prison following his original conviction in November 2013.

One of Blackman's legal team indicated he would probably be released in about two weeks, but the decision on the exact date is for the Prison Service to determine.

The Court Martial Appeal Court ruled previously that Blackman was suffering from an "abnormality of mental functioning" at the time of the 2011 killing when he was serving with Plymouth-based 42 Commando.

The court found the incident was not a "cold-blooded execution", as a court martial had earlier concluded, but the result of an "adjustment disorder".

Mrs Blackman said her husband's release "can't come soon enough" and stressed that lessons must be learned from his case.

"There are huge lessons to be learned from this case in so many aspects, from the court martial process itself, through to the way that our servicemen and women are supported during particularly stressful circumstances," she told BBC Radio 4's Today.

Her husband had "never denied that his actions on that day were caused by a serious lack of judgment, which we now know to be due to a combat stress disorder", she said.

"He has always regretted his actions, if he could turn the clock back and undo that moment he would do, in a heartbeat."