Ulster Unionist MLA Mike Nesbitt has revealed how he told Martin McGuinness that he hated what he had done by having been in the IRA.
The Strangford representative said the forthright exchange came in 2013 as the two men took an hour-long walk around the grounds of Stormont.
Mr Nesbitt was then leader of the Ulster Unionist Party.
He said he quickly realised they were never going to agree about the past.
During his life, Mr McGuinness said he had been a member of the Provisional IRA until 1974.
He was described during the Saville Inquiry as being second in command of the Londonderry brigade of the PIRA at the time of Bloody Sunday in 1972.
In 2012, he shook hands with the Queen.
Mr McGuinness went on to rise through the ranks of Sinn Fein and served as deputy first minister of the Northern Ireland Assembly until January 2017 when he resigned in protest over the DUP’s handling of an energy scandal.
The move effectively collapsed the powersharing institutions, which remain dormant now.
Mr McGuinness died at the age of 66 in March 2017 after battling a rare heart condition.
“I said I hated what he did by being in the IRA,” Mr Nesbitt said.
“I really resent the fact that he said unionism left him with no option.
“I said, ‘Martin, if you pick up a gun, you made a choice’.
“He said, ‘But you didn’t live the life I did’.
“If he had gone as far as to say he made the choice, but he didn’t.”
“That’s when we agreed to disagree.”
Mr Nesbitt said that he and Mr McGuinness spent the rest of their walk talking about the future.
There was even a lighter moment when they met a couple of Chinese tourists and spent some time talking to them.
He said he met Mr McGuinness another three times privately in his office without any advisers around.
Speaking during the Warm House for Unionists panel debate at the West Belfast Festival on Thursday evening, Mr Nesbitt described Mr McGuinness as a man of “political integrity” after he kept views expressed confidential.
“We were able to discuss sensitive issues,” he said.
“If he had gone public, saying this is what Mike Nesbitt thinks, it would have caused me some grief.
“He did show some political integrity by choosing to respect the confidentiality of the conversation.”