Harry, King Charles' younger son, is one of more than 100 high-profile figures suing the Mirror Group Newspapers (MGN), the publisher of the Daily Mirror, Sunday Mirror and Sunday People, for alleged phone-hacking and other unlawful behaviour between 1991 and 2011.

He had been expected to attend court on Monday morning but failed to appear. The judge, Timothy Fancourt, said he was "surprised" and MGN's lawyers described his absence as "absolutely extraordinary".

However, the prince will face hours of questioning in the witness box on Tuesday becoming the first senior British royal to give evidence in court for 130 years.

The trial began last month, as lawyers representing Harry and three other test claimants attempted to prove that unlawful information gathering was carried out with the knowledge and approval of senior editors and executives.

Harry's allegations are the focus this week, and his lawyer David Sherborne on Monday said the motivation for bringing the lawsuit was to shift "the attention that comes with his position on these activities".

Unlawful information-gathering was carried out "not just by (MGN) journalists, but they have been concealed even though they were known about by senior members of the board of this Plc (company), as well as the legal department," Sherborne added.

Harry's life was "invaded by these three newspapers using unlawful methods and it is the use of these methods by a national media group that has brought him here, not some vendetta against the press generally", the lawyer said.

MGN's lawyer Andrew Green said there was no evidence that Harry's phone was hacked once, let alone habitually, and none of those who had admitted illegally listening to voicemail messages said they had targeted the prince.

PRINCESS DIANA 'HACKED'

Outlining Harry's case, Sherborne said some 2,500 articles had appeared about Harry's private life in the MGN titles during the period the allegations covered, from when he was a young boy at school through to the death of his mother in 1997, his later military training and adult life.

"Nothing was sacrosanct or out of bounds and there was no protection from these unlawful information-gathering methods," Sherborne said.

He also suggested Diana's phone had been hacked, referring to handwritten letters she had sent to a well-known TV presenter, Michael Barrymore, which detailed secret meetings between them after he had publicly disclosed he was gay.

In one letter, sent months before her death, she said she was devastated that the Daily Mirror had been contacting her office to ask about the meetings.

"Plainly the Daily Mirror has been listening in to voicemail messages," Sherborne said. Green said that was total speculation made without any evidential basis.

Sherborne also accused MGN of engendering the "mistrust" between Harry and his brother William, the heir to the throne, with whom he has had a high-profile falling out in recent years since Harry and his American wife, Meghan, stepped down from royal duties and moved to the United States

An article from 2003 about the brothers disagreeing over how to treat their mother's former butler showed "the seeds of discord between these two brothers are starting to be sown", Sherborne said.

ROYAL AIDES IN FOCUS

MGN, now owned by Reach (RCH.L), has previously admitted its titles were involved in phone-hacking and has settled more than 600 claims at a cost of more than 100 million pounds ($120 million) in damages and costs.

It apologised at the start of the trial after admitting on one occasion the Sunday People had unlawfully sought information about Harry. But, Green said there was nothing to suggest any other unlawful activity relating to the royal.

In court documents, MGN said some information had come from royal aides.

This week's appearance will be the second time this year Harry has attended the High Court, after joining singer Elton John and others for hearings in March over their lawsuit against the publisher of the Daily and Sunday Mail tabloids.

Harry, the fifth-in-line to the throne, is engaged in several legal battles with the British press, including a similar phone-hacking case against Rupert Murdoch's British newspaper arm.

The prince has also accused his family and their aides in his memoir and Netflix documentary series of colluding with tabloids. The palace has not commented on those accusations.