Piers Morgan's Daily Mirror allegedly hacked the Princess of Wales' phone in order to acquire information on her secret meetings with comedian Michael Barrymore.

The high court heard that Lady Diana had chatted to Barrymore on a frequent basis in the months leading up to her death when they were two of Britain's most renowned persons.

On Monday, a phone-hacking trial heard excerpts from a letter in which Diana pledged to help Barrymore. In one letter, sent in early 1997, the Princess supplied her phone number and emphasized that she would be there for him whenever. 

“It’s very easy to pop round and see you or please telephone now you have my number. You’re doing just fine and believe me, I know. So take great care and lots of love from Diana.”

Diana rewrote months later, saying she was "devastated" that the Daily Mirror had received information of their ostensibly private encounters. She apologized to Barrymore for the leak, lamented her "nightmare time with the tabloids," and claimed she had no idea how the story got out because "nobody knew about our conversations." According to the court, Barrymore did not respond to this letter, emphasizing the "isolation" created by journalistic interference.

The obvious explanation, according to David Sherborne, the attorney representing Diana's younger son, Prince Harry, in the trial against Mirror Group Newspapers (MGN), is that the Daily Mirror hacked his mother's voicemails.

The lawyer also alleged that Piers Morgan, the paper's then-editor, was dishonest when he later stated in his memoirs that he had "heard rumors" about Diana and Barrymore's friendship.

Sherborne stated that the reason Morgan heard such stories was that "the Mirror had been listening in on her messages."

The Mirror has responded to the accusations by saying the hackings were "total speculation without any evidential basis whatsoever," and Morgan has denied having had any knowledge of the hacking.

The lawyer representing the publication,  Andrew Green KC, detailed to the court that the letters are not evidence of voicemail interception.

The claim was made during the ongoing phone-hacking trial of Mirror Group Newspapers. On Monday, the court began delving into the intricacies of Harry's lawsuit against MGN.

The court has been hearing testimony concerning the overall culture at the Daily Mirror, Sunday Mirror, and People for three weeks. Harry claims that the publications used phone hacking and other unlawful information-gathering practices against him.

Sherborne detailed articles about Harry being analyzed as part of the case, including a "web" of illegal activity. According to the lawyer, the prince was distressed by how his relationship first serious girlfriend Chelsy Davy fell apart due to pressure from the tabloids and feeling like they were "never on their own."

The Mirror has admitted that it engaged a private investigator to unlawfully obtain information on Harry's 2004 visit to a nightclub. However, it argues that its other publications about him were obtained legally, through sources offering information and royal press officials briefing stories.

Green stated that in the mid-2000s, the Metropolitan Police investigated the hacking of Harry's voicemails. They discovered evidence that journalists at Rupert Murdoch's News of the World had accessed the prince's voicemails, but no proof that journalists at the Mirror group were involved in the criminal activity. According to him, the whole case of Harry lies on the premise that a Sunday Mirror reporter had his phone number in his contacts.

According to Green, Harry's claims are supported by “Zilch, zero, nil, de nada, niente, nothing" of evidence. 

On Tuesday morning, Harry will begin presenting testimony from the witness stand.