Former Black Caps captain Brendon McCullum has opened up for the first time about his involvement in the Chris Cairns trial, describing it as a "horrible" experience.
Last year Cairns was tried for perjury and attempting to pervert the course of justice.
He was found not guilty on all charges, after an eight-week trial in London.
In an in interview with TVNZ 1's Seven Sharp, McCullum says he has no regrets about his decision to testify against his former teammate.
"Whether they believed me, whether they didn't. None of that really matters. It wasn't about a guilty or not guilty verdict. It was a matter of fulfilling a moral obligation I felt I had."
McCullum and Cairns played together in the Black Caps, where they became friends.
Brendon McCullum arrives at Southwark Crown Court to give evidence in the trial of New Zealand cricketer Chris Cairns on October 15, 2015
"He was everyone's hero back then," says McCullum, "but it's dangerous when you meet your heroes, I guess".
McCullum claimed that Cairns approached him about match-fixing in 2008. It took three years for him to make a statement to cricket officials.
"I just simply didn't understand that if you weren't to report it, you were just as in the gun as anyone that has actually approached you," says McCullum. "Once I realised that, I straight away went and reported it".
Chris Cairns, former New Zealand cricketer, leaves Southwark Crown Court on October 7, 2015 in London
When Cairns was put on trial, McCullum flew to London to testify in front of a jury. Other witnesses included cricketers Lou Vincent and Shane Bond.
"I didn't have to testify," he told Seven Sharp. "I think that's something that people don't understand. And I'm pretty sure lots of people wouldn't do what I did. But I felt I had an obligation, especially as captain of New Zealand, to go over and tell my side of the story."
I guess I can never forgive him for that"
McCullum's confidential statement to cricket bosses had been leaked to the press, and he was criticised in the media for being disloyal to Kiwi cricket.
"I was prepared to stand up, even under pressure and under fire from various quarters, and do what I thought was morally right at the time.
"The last thing I wanted to do was be in a courtroom testifying against one of my old mates. It's certainly not how I was brought up as well."
Former New Zealand cricketer Chris Cairns arrives at Southwark Crown Court on November 24, 2015
Cairns was found not guilty on all charges in 2015. Outside court, he was asked what his message was for Brendon McCullum. Cairns simply said: "Why?"
McCullum says the fact that the court case became "about me versus [Cairns] is something I'll never understand".
"Under pressure, people show their true character. It's not the character I thought I knew, and I guess I can never forgive him for that".
Tomorrow, McCullum will release his autobiography, Declared, in which he writes a letter to Cairns, addressing him as "Cairnsy".
Brendon McCullum arrives at Southwark Crown Court to give evidence in the trial of New Zealand cricketer Chris Cairns
He told Seven Sharp that he has moved on from the Cairns case. In terms of how he feels about Cairns now: "I'm sure he'll get on with his life, and I'll get on with mine, and let's hope they never cross paths"
McCullum says he'd rather be remembered for his achievements on the cricket pitch, including his triple-century at the Basin in 2014.