The Canberra Times has chosen not to name the man, but can reveal his family's dark legacy as both parents serve lengthy sentences for ''profoundly evil behaviour''.

Now their son is facing the prospect of a long custodial sentence for his own crimes committed against a former partner in July last year.

The 29-year-old yesterday pleaded guilty in the ACT Magistrates Court to a dozen charges stemming from the ordeal at the south Canberra apartment.

The Griffith man broke into the flat armed with a knife, held the woman against her will and raped her multiple times.

He will be sentenced on seven counts of having sexual intercourse without consent and a charge of sexual assault in the third degree - threatening harm in order to have sex with a person.

The man has also been charged with unlawful confinement, assault, aggravated burglary and committing an act of indecency without consent.

He was yesterday committed for sentence in the ACT Supreme Court, and his lawyer noted a lengthy prison sentence was likely.

If incarcerated he will join his 57-year-old father and 58-year-old mother, both locked up in 2010 for molesting their two daughters.

ACT Supreme Court Chief Justice Terence Higgins jailed the father for 20 years in 2010, and he will be eligible for parole after serving 15.

At the time it was one of the longest sentences handed down in the territory in years.

The mother will be eligible for release in 2015 after serving half of her 10-year sentence.

The pair sexually abused the girls throughout the 1980s and 1990s at the family home in Canberra's north.

The victims were molested as often as every two days for years and were only allowed out of the house on grocery shopping trips. One of the girls, in a distressing victim impact statement tendered during her parents' sentencing proceedings, described their home life as ''rotten to its dysfunctional core''.

The abuse finally ended when the victims left the family home in 1996, and was reported to police in 2005 and 2006.

''The sexual abuse of these two courageous women ... started when they were young children and continued until they were young women when they could only then escape,'' the judge wrote in his sentencing remarks.

Chief Justice Higgins described the father, in particular, as ''the instigator of profoundly evil behaviour''.

The father dropped an appeal against his 20-year sentence in November after the Court of Appeal warned it was considering locking him up for even longer.

Magistrate Beth Campbell adjourned the son's case until February, when he will face the Supreme Court for sentencing.

He remains in custody.