Serial paedophile Ian Harold King, 79, pleaded guilty in the ACT Magistrates Court on Monday to a charge of committing an act of indecency on a child.

King entered the plea via audio-visual link from the Alexander Maconochie Centre, where he is already serving child sex offence sentences totalling nearly 22 years.

Some of his previous offending involved him having boys he coached stand in front of a mirror and strip off while he pointed out muscles that required development.

King would then touch the boys, which is what he did with the 13-year-old he has now admitted to abusing in September 1998.

Agreed facts show the victim met King when the former Queensland first-class cricketer, who also boxed under the name "Young Rainbow", was a selector for the ACT Comets.

"Kingy", as he was known in the cricketing community, was also a coach at the Ginninderra Cricket Club, where the boy played.

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King offered the boy private coaching sessions and the victim accepted, believing the renowned fast bowler would help his career development.

One day in September 1998, King picked the victim up and trained him at Phillip Oval before they had lunch and drove to the offender's home in Lyons.

In the apartment, King showed the victim a diagram of the human body and had him stand in front of the mirror, where he instructed the boy to take off his clothes.

"The victim felt frightened, humiliated and frozen," the agreed facts state.

King then touched the boy inappropriately and performed a sexual act on him.

"This was the victim's first sexual experience," the facts say.

"The victim felt ashamed, embarrassed and humiliated."

The victim, by then an adult, disclosed the incident to his wife in 2019 after becoming aware of the national redress scheme for victims of child sexual abuse, to which he made an application.

He later spoke to his father and sister about it, then participated in an interview with police in October last year.

The matter made its way to court earlier this month but King, who lost an eye during a prison bashing described as "sickening", did not appear on that occasion.

He was originally charged with two offences, one charge was withdrawn on Monday following his guilty plea.

Magistrate Robert Cook committed King to the ACT Supreme Court for sentence, with the case first listed there on Thursday next week.

King's current jail sentence does not expire until July 2030, but he became eligible for parole in 2020.

His current non-parole period will be cancelled and reset when he is sentenced again.

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