"The reality of a recount swinging Northland back in my favour is beyond a tall order when looking at how recounts have gone in the past," he said on Facebook.
"I have called Willow Jean Prime and congratulated her on being elected as the MP for Northland.
"It has been the honour of my life to represent the place I am so proud to call home ... Thank you Northland, it's been a blast."
King will be in Wellington on Tuesday to offer his final remarks to the National Party caucus.
On election night, King won 15,337 votes, 729 ahead of Prime's 14,608.
However, the final result shows Prime got 17,066 votes, compared to King's 16,903, for a 163 vote majority.
Prime was ecstatic in the minutes after hearing the news she had taken the electorate - the first time Labour has done so since 1938.
"I was shaking when I found out," Prime said. "I can't believe it. It is a dream come true."
Prime was well aware of the 82-year gap since Labour had won an earlier iteration of the electorate. The seat of Bay of Islands was won by teacher and trade unionist Charles Boswell for a single, extended, wartime term.
"I have humbled so many people voted for me," Prime said.
"I had always tried to be the best voice and representative for Northland in Parliament whether I'm a list or electorate MP.
"I knew when I put my hand up in 2014 it was going to be one hell of a battle in such a safe blue seat. It's been a roller coaster ride with so many twists and turns. I will continue to do the best I can for Northland."
