The Duke of Sussex unexpectedly appeared at the High Court as legal proceedings began over alleged phone-tapping and other breaches of privacy.
Prince Harry, who is one of those suing Associated Newspapers, the publisher of the Daily Mail, was joined in the court room by singer Sir Elton John.
The duke, who was last seen in the UK for the Queen’s funeral, claims he was left feeling “suspicion and paranoia”.
The publisher “vigorously denies” all the claims against it.
Prince Harry arrived at the High Court on Monday morning, while Sir Elton, who is also involved in the legal proceedings, joined proceedings at lunchtime.
The pair, along with actresses Sadie Frost and Liz Hurley, are among the individuals who allege unlawful information gathering by the company, which also publishes the Mail on Sunday.
Others taking part in the legal action include Sir Elton’s husband David Furnish, and Baroness Doreen Lawrence, the mother of Stephen Lawrence, who was murdered in a racist attack in 1993.
The four-day preliminary hearing in London is considering legal arguments and a judge will decide whether the case will go any further. Associated Newspapers (ANL) wants to end the claims without trial.
David Sherborne, the lawyer for the group of prominent individuals, said: “The claimants each claim that in different ways they were the victim of numerous unlawful acts carried out by the defendant, or by those acting on the instructions of its newspapers, the Daily Mail and the Mail on Sunday.”
He said the alleged unlawful activity included “illegally intercepting voicemail messages; listening into live landline calls; obtaining private information, such as itemised phone bills or medical records, by deception or ‘blagging'”.
The activity also allegedly included “using private investigators to commit these unlawful information gathering acts on their behalf and even commissioning the breaking and entry into private property”.
He added: “They range through a period from 1993 to 2011, even continuing beyond until 2018.”
Prince Harry had “suspicion and paranoia” caused due to the publication of articles by ANL using unlawfully gathered information, the High Court was told.
Mr Sherborne said he was “troubled that, through Associated’s unlawful acts, he was largely deprived of important aspects of his teenage years”.
The barrister said: “Friends were lost or cut off as a result and everyone became a ‘suspect’ since he was misled by the way that the articles were written into believing that those close to him were the source of this information being provided to Associated’s newspapers.”
He added: “The claimant regards Associated’s unlawful acts to amount to a major betrayal given promises made by the media to improve its conduct following the tragic and untimely death of his mother, Princess Diana, in 1997.”
The High Court was told Sir Elton and Mr Furnish’s landline at their home in Windsor was tapped by a private investigator on the instructions of Associated Newspapers Limited.
Mr Sherborne said they were “mortified to consider all their conversations, some of which were very personal indeed, were tapped, taped, packaged and consumed as a commercial product for journalists and unknown others to pick over regardless of whether or not they were published”.
The High Court heard Sir Elton and Mr Furnish had not seen a copy of their first child’s birth certificate before it was unlawfully obtained by ANL.
Mr Sherborne also told the court a private investigator acting on behalf of ANL hacked Hurley’s phone and placed a “sticky window mini-microphone” outside her home.
He added her ex-boyfriend Hugh Grant’s car was bugged to unlawfully obtain information about her finances, travel plans and medicals during her pregnancy.
He also told the court ANL paid a private investigator to unlawfully find the address of a man it believed was the male lover of Liberal Democrat politician Sir Simon Hughes.
Baroness Lawrence’s bank accounts were monitored to check whether she was receiving any money from other newspapers during the Daily Mail’s Justice for Stephen Lawrence Campaign, Mr Sherborne alleged.
“She finds it hard to believe the level of duplicity and manipulation that was clearly at play, knowing now as she does that the Daily Mail’s outward support for her fight to bring Stephen’s killers to justice was hollow and, worse, entirely false,” he said.
ANL has said it categorically denies the serious claims made in the litigation and will vigorously defend them if necessary.
The group launched the legal action last year. ANL’s lawyer Adrian Beltrami KC said, in written submissions, that the legal actions had been brought too late, were “stale” and the claims were “largely inferential”.
The barrister said the individuals had to prove they did not know earlier, or could not have discovered earlier, they might have had a claim against ANL for alleged misuse of their private information.
He said none of the group said they believe they continued to be targeted by unlawful information-gathering after 2015.
In a statement after Monday’s hearing, it added: “A private investigator whose ‘confessions’ form a key element of a privacy case being brought against Associated Newspapers by Prince Harry, Baroness Doreen Lawrence, Elton John and others has denied their allegations that he acted illegally against them on behalf of the Daily Mail or Mail on Sunday.”
It said while the Mail’s admiration of Baroness Lawrence remained undimmed, we are “profoundly saddened that she has been persuaded to bring this case”.
It added: “The Mail remains hugely proud of its pivotal role in campaigning for justice for Stephen Lawrence. Its famous ‘Murderers’ front page triggered the Macpherson report.”
The hearing continues on Tuesday.