Malcolm Powys, who was the head of the elite school's Highton campus between 1993 and 1997, said he had been "sickened" to discover the extent of the abuse perpetrated by Phillippe Trutmann, who worked as a boarding house assistant between 1985 and 1995.

In 2005 he was convicted of sexually abusing at least 40 male students between 1985 and 1995, and sentenced to six-and-a-half years' jail.

Mr Powys removed Trutmann from his position in 1996, after being made aware of repeated complaints by fellow staff members about Trutmann's behaviour.

On Friday, Mr Powys told the Royal Commission into Institutional Responses to Child Sexual Abuse that he removed Trutmann because of concerns that Trutmann was reading stories to boys at night behind closed doors, but agreed with a suggestion that those concerns probably went further.

However, he said, he did not know what was going on behind closed doors.

"It has been a disturbing and sickening revelation to me," he said, choking up with tears.

"How could this have happened? What did I miss? What else might I have done to stop him?

"Here and now I offer my personal and unreserved apology to any student who was sexually abused by Trutmann under my watch. … I should have known what was happening. I did not. I am deeply sorry that you suffered so profoundly at Highton under my leadership.

"It was not your fault that you were abused. You did nothing to attract Trutmann's attention. You were young, you were vulnerable; you should have been safe. You were not safe. We should have had better measures in place to prevent Trutmann's sexual abuse....I am extremely sorry that I failed to protect you from this man."

Also on Friday, the former deputy to the master of Highton campus, Paul Claridge, told the commission he had held suspicions about Trutmann's abuse of children, but had had no evidence to back his suspicions.

"At the back of my mind the unease was that he may have been [acting inappropriately], but there was absolutely no clear evidence and that's the difficulty of the case I think."

In 1989, staff reported to Mr Claridge that a student had told of being sexually assaulted by an unknown man while he slept.

Mr Claridge agreed that the perpetrator could only have been one of two men, but said he did not go to the police about the report.

"It was clearly a matter for reporting to the relevant authority within the school, who would then investigate and report to the police or any other agency that was appropriate once they completed an investigation; that was my thinking."

Police were never informed.

The hearing continues.