According to the Guardian article, only the Duke of Sussex is suing, and his libel claim is "reportedly" (reported by whom?) related to this article by Kate Mansey in the Mail on Sunday and MailOnline, published on February 19.
https://www.dailymail.co.uk/news/ar...arry-tried-legal-fight-bodyguards-secret.html
Victoria Ward of The Telegraph reports:
The Duke’s legal firm, Schillings, has alleged that the claims he lied about offering to pay for his protection and that he wanted the existence of the litigation to remain confidential are false and defamatory, the Telegraph understands.
https://www.telegraph.co.uk/royal-f...ches-libel-case-against-daily-mail-publisher/
Quoting the Mail article, it would seem that this is the allegedly false and defamatory claim "that he wanted the existence of the litigation to remain confidential":
Prince Harry tried to keep details of his legal battle to reinstate his police protection secret from the public, The Mail on Sunday can reveal.
High Court documents show he sought a far-reaching confidentiality order on documents and witness statements surrounding his case against the Government.
But the Home Office argued for transparency, saying 'there must be a sufficiently good reason, in the wider public interest, to justify the departure from open justice that such an order involves'.
Both sides then agreed that some papers would be made public with the Home Office agreeing to carry out a 'confidentiality exercise' to determine what would be kept secret, even though it caused 'an unprecedented expenditure of time and resources'.
And this would seem to be the allegedly false and defamatory "[claim] he lied about offering to pay for his protection":
When The Mail on Sunday last month revealed that Harry was suing the Government, his spin-doctors swung into action, briefing journalists that Harry was being denied the right to pay for bodyguards.
It led to inaccurate reports across the media, such as the BBC headline: 'Prince Harry in legal fight to pay for UK police protection.'
As documents lodged at the High Court last week show, no such offer to pay was made in the Prince's initial 'pre-action' letters to the Home Office, suggesting he expected British taxpayers to cover it.
The revelations are a crushing rebuttal to Harry's initial public statement that implied he had always been willing to foot the bill.
Nor did he offer to pay when he visited the UK last June to unveil a statue to his mother, Princess Diana.
Home Office lawyers state that it was only in later correspondence that the offer was made.
Yet his initial bid to get the decision overturned did not mention he would pay anything. Court papers say: 'The offer [to pay] is now advanced in the Claimant's witness statement...but notably was not advanced to RAVEC in June 2021 or in any of the pre-action correspondence which followed.'