Former Downing Street press secretary Alastair Campbell says he always knew journalist Roy Greenslade was a supporter of a united Ireland.
Mr Greenslade is a veteran British journalist and media commentator.
In a recent article for the British Journalism Review, he opened up about his 'covert political beliefs' - including how he wrote columns for Sinn Féin newspaper An Phoblacht under the pseudonym George King.
He says he has a 'passionate wish' to see a united Ireland, and that he was 'convinced of the IRA’s political ambitions' during the 'war' of the 1970s (noting he began to 'doubt its bombing tactics' over the years).
There has been a major fallout to the news across British and Northern Irish media.
Mr Greenslade's former long-time employer The Guardian is reviewing a complaint by Máiría Cahill about an article written by the journalist about her in 2014.
Ms Cahill has accused him of demonising her in the column, which was responding to a BBC documentary in which she detailed her allegations that she was raped by an IRA member.
The Guardian said it will also look at all articles Mr Greenslade wrote about Northern Ireland to ensure its editorial standards were met.
Mr Campbell spoke to The Pat Kenny Show about the revelations.
He said: "I always knew he was basically a supporter of a united Ireland... whether I would have ever said he was a supporter of terrorism, no.
"I've not read the whole piece - I'm always a bit wary with these kind of flurries of excitement.
"He's written this long piece in the British Journalism Review, which I think I think I will read before I join in the ritual condemnation.
"Certainly, I always knew that Roy was a supporter of a united Ireland."
However, he added that many people who currently edit British national newspapers 'do a hell of a lot of damage' to the UK as well.
