Diana, Princess of Wales, would be “incredibly touched” and “rightly proud” of the Duke of Sussex for taking on News Group Newspapers (NGN) and gaining an apology for its serious intrusion into her private life, her brother has said.

Charles Spencer praised his nephew after Prince Harry received a full and unequivocal apology and “substantial damages” from the publisher over “serious intrusion” by the Sun, including unlawful activities by private investigators working for the paper.

Harry, 40, alleged he was targeted by journalists and private investigators working for NGN and the now-defunct News of the World. In a statement, NGN also apologised for the impact of the “serious intrusion” into the private life of Harry’s late mother, Diana.

“It takes an enormous amount of guts to take on opponents like News Group Newspapers, and great tenacity to win,” Earl Spencer posted on X. “And it’s just wonderful that Harry fought for – and gained – an apology to his mother. She would be incredibly touched at that, & rightly proud.”

NGN’s apology marked the first time unlawful activities at the Sun were admitted, Harry’s legal team said.

The duke’s barrister, David Sherborne, said in a statement outside court: “In a monumental victory today, News UK has admitted that the Sun, the flagship title for Rupert Murdoch’s UK media empire, has indeed engaged in illegal practices. This represents a vindication for the hundreds of other claimants who were strong-armed into settling, without being able to get to the truth of what was done to them.”

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Prince Harry's lawyer says settlement is 'monumental victory' – video

The former deputy Labour leader Tom Watson also settled his claim after he was offered a “full and unequivocal” apology and substantial damages for “unwarranted intrusion” into his private life during his time in government by the News of the World.

The settlement of both cases was announced as the trial stage of Harry’s five-year legal action over unlawful information gathering by NGN was due to open at the high court in London.

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The duke and Lord Watson are calling for a police and parliamentary investigation into “not only the unlawful activity now finally admitted, but the perjury and cover-ups along the way”, Sherborne, who represented both claimants, said on Wednesday.

Watson said after the hearing that a “dossier exposing wrongdoing” would be submitted to the Metropolitan police.