Peter FitzSimons wore a white linen suit as he entered the witness box in a Sydney court on Thursday to testify in Jones's trial on 22 charges of indecent assault and sexual touching without consent.
He told the court he first came into contact with Jones when the older man was a rugby union coach seeking to poach him for a Manly team in 1982.
FitzSimons later praised Jones, who went on to direct the national Wallabies team, as an "absolutely brilliant" coach in a print article.
But he agreed he had also accused Jones of bullying, lying, and having agendas in print.
"Alan Jones is a malignant tumour on the body politic of this city, this state and this country and the sooner he is excised the better," he wrote in a 2018 article.
When asked about the line on Thursday by Jones's barrister Gabrielle Bashir SC, FitzSimons said he was "very proud of that" and stood by it.
"You were at that time, and you remain, publicly and unashamedly anti-Jones," Ms Bashir suggested.
"Almost proudly," he replied.
Ms Bashir previously argued Jones's media rivals are deeply involved in the case against him, which she says is characterised by rivalry, hatred, and double dealing.
Jones's rival and prominent radio broadcaster Ray Hadley put FitzSimons in touch with a former radio staffer who had disclosed alleged indecent assaults by Jones.
He knew FitzSimons had been researching similar allegations about Jones at the time and had offered him background information, the author told the court.
Jones faces eight charges in relation to the radio staffer, who claims he was subjected to unwanted kisses in lifts and groped while driving and at an event.
FitzSimons said the young man broke down in tears and was deeply upset when confiding in FitzSimons about the alleged indecent assaults years later.
The complainant had described Jones as "the most important, the most powerful person at 2GB" - Sydney's No.1 radio station at the time - and recalled how he had been drawn into his orbit, FitzSimons said.
"Mr Jones had noticed his work, complimented him, drawn him in," he told the court.
"Mixed in with the compliments were the occasional blasts."
He said the complainant confided he had been driving when Jones put his hand on his knee and moved it to his groin to stroke his genitals, before he pushed it away.
"He made it absolutely clear he was revolted at what happened but he was also deeply upset at himself for not being stronger," FitzSimons said.
"He was very, very upset.
"It was clear I was speaking to somebody who was completely emotionally traumatised."
Under cross-examination, he accepted that his police statement placed Jones's hand on the man's thigh instead, quipping that the difference was "a matter of inches".
He said the alleged victim also recounted getting into a lift at Jones's Circular Quay home with fully laden hands and the veteran broadcaster pushing him against the wall, grabbing his groin, and kissing him "romantically".
When he learned the man was panicking and spiralling after the phone conversation, FitzSimons said he wouldn't take the allegations any further.
He had been unable to go to police about the allegations because he didn't know the man's identity, he said.
FitzSimons took a long look at Jones while facing him from the opposite side of the room, but the longtime shock jock appeared determined to avoid locking eyes.
The 85-year-old retired broadcaster has pleaded not guilty to all charges, which are alleged to have occurred between 2003 and 2020 across Sydney and the NSW Southern Highlands.
Jones, whose 35-year career spanned TV and radio, has dismissed the allegations by the six complainants as false.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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