A child migrant sexually abused by Catholic brothers in Perth has testified he was raped by his school principal after reporting the abuse.

Key points: The man claims he was abused by three Christian Brothers and then reported it to the school principal, who bashed and raped him

The man claims he was abused by three Christian Brothers and then reported it to the school principal, who bashed and raped him The principal, Brother Patrick O'Doherty, has since died

The principal, Brother Patrick O'Doherty, has since died The case is the first of its kind to go to trial since WA removed a statute of limitations on child sexual abuse

WARNING: This story contains material that some readers may find upsetting

The man, who cannot be identified, was a student at the Christian Brothers Castledare and Clontarf orphanages in the 1950s and 1960s.

He has given evidence in a trial being brought against the Christian Brothers by another child sexual abuse survivor, John Lawrence.

The man has testified he was abused by three Christian Brothers and reported it to the school principal at Clontarf, Brother Patrick O'Doherty, who then accused him of lying and bashed him.

The man said sometime later Brother O'Doherty, who is now dead, told him he would give him a sex lesson and subjected him to rape.

John Lawrence said the abuse he suffered as a child at the hands of a Christian Brother made him feel "dirty" and "worthless". ( ABC News: Hugh Sando )

He said it was the first of four times that Brother O'Doherty raped him.

He told the court that after each rape the principal told him not to tell anyone, warning him that if he did he would be in "very serious trouble".

One of the brothers, James Murray, admitted to abusing the man before he died.

The man has never told his family about the abuse.

The homestead of the Castledare Boys' Home in Wilson, Perth, run by the Christian Brothers. ( Wikimedia: Moondyne )

The Christian Brothers case is the first of its kind to go to trial since Western Australia removed a time limit restricting when child sexual abuse cases could be brought.

The trial has already heard how Mr Lawrence was repeatedly raped as a nine-year-old boy by Brother Lawrence Murphy.

A similar case brought by a terminally ill man, Paul Bradshaw, was settled for $1 million before proceeding to trial in 2018.

Earlier, the court heard from David Watson, a doctor who had examined Mr Lawrence.

He testified it did not surprise him that Mr Lawrence had poor literacy and numeracy skills given Brother Murphy was also his teacher.

Dr Watson praised Mr Lawrence's former wife for teaching him reading and writing.

The trial continues.