Prince Harry's lawyers have alleged the Sun unlawfully targeted Meghan Markle via a private investigator.
The Duke of Sussex's lawyers told the High Court an investigator provided information in 2016 for two stories on the future Duchess of Sussex.
These stories were published shortly after Prince Harry and Ms Markle started their relationship.
News Group Newspapers (NGN) - which owns the Sun - deny the allegations, with a trial set for January 2025.
In the second day of a three-day hearing in Prince Harry's battle to sue NGN, the duke's lawyers also alleged the company paid investigators to intercept landline calls relating to the duke.
Last year the High Court ruled Prince Harry had run out of time to bring a case against the Sun's owner for phone hacking.
His wider allegation of unlawful information gathering by other means is however likely to go to trial in January.
PA MediaPrince Harry's lawyers are seeking permission to update parts of his case
Ahead of that, a High Court judge must rule whether the duke can add to his range of allegations.
Prince Harry's lawyers are seeking permission to update parts of his case, but NGN's barristers have argued changes to claims are "wholly unnecessary".
Court papers released on Thursday show Prince Harry now wants to sue over 235 stories which appeared in the Sun and the now defunct News of the World.
The earliest date from when he was nine years old, in 1994, and the last two items concern the early days of his relationship with Ms Markle in 2016.
'Smitten prince'
Those final two stories, the court was told, concern alleged admissions from a US private investigator, first made to the BBC in 2021.
Danno Hanks told the BBC he obtained detailed private information about Ms Markle including her social security number, mobile phone number and had compiled a dossier of facts about her life for the Sun.
At the time, the Sun said it had only ever requested legitimate research and instructed Mr Hanks to act within the law.
The Sun said it at no time asked Mr Hanks for her social security number and it did not use the information he provided for any unlawful practice.
Legal papers in the case say the Sun used information provided by Mr Hanks for two stories about the new couple.
One of the stories reported the "smitten" prince had bombarded the then Ms Markle with text messages.
"On 31 October and 1 November 2016, The Sun published two articles by Emily Andrews and James Beal concerning the claimant's relationship with Meghan Markle," the High Court was told in written submissions.
"The claimant will contend that in late October 2016 the Defendant (through the journalist, James Beal) instructed an American private investigator, Danno Hanks... to obtain private information in the form of a report on the claimant's new relationship with his now wife.
"It can be inferred that the mobile number of the duchess obtained by Mr Hanks ... was then used to obtain private information about the frequency of text messages between the Claimant and the duchess."
The Sun says that allegation is untrue and, if the claim is included in the eventual trial, it will fight it.
David Sherborne is the lawyer representing Prince Harry
Reuters
It has also emerged while the duke cannot sue over mobile phone hacking, he now wants to claim damages for the alleged interception of landline calls "including by the use of scanning devices and the placing of bugs".
In written submissions, Anthony Hudson KC, for NGN, said the duke's new allegations should be dismissed by the judge because they were "wholly different" to his original claims.
He argued allegations concerning the two Ms Markle articles could not be considered because they are matters for US law.
Some of the other allegations lacked any supporting evidence that journalists had been involved in wrongdoing.
The hearing continues on Friday, and Mr Justice Fancourt is expected to rule later on what will be included in next January's trial.
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