Prince Harry was feeling "confident and ready" ahead of the start of his civil trial against a newspaper publisher this morning.

The Duke of Sussex appeared at London's High Court for the beginning of the trial against Associated Newspapers Limited, the publisher of the Daily Mail, the Mail on Sunday and Mail Online.

Along with Elton John and his husband David Furnish, Elizabeth Hurley and Sadie Frost, and other claimants, Prince Harry is suing the publisher over allegations of unlawful information gathering, such as phone hacking.

Before the trial began, a spokesperson for the royal told People that he is "feeling confident and ready" as the long-running case moves forward.

The trial is expected to last nine weeks, and the 41-year-old is slated to be the first witness to take the stand on Thursday.

Frost, Hurley and her son Damian also attended court on Monday, while John and Furnish said in a written statement that their home was "violated" by alleged illegal news gathering, reports BBC News.

In his opening statements, barrister David Sherborne, representing all seven claimants, declared that he intends to prove that "there was clear, systematic and sustained use of unlawful information gathering at both the Daily Mail and the Mail on Sunday".

He argued that there is "no way" some of the details reported, such as private phone numbers, flight tracking details and travel plans, could have been obtained lawfully.

Prince Harry alleges that 14 articles published by Associated Newspapers titles between 2001 and 2013 used unlawfully gathered information about him.

The Associated Newspapers team has "vigorously denied" the claims and will also argue that he left it too late to pursue his case.

Harry, who lives in California with his wife Meghan and their two children, has previously sued two other newspaper publishers over alleged illegal information gathering.

His case against The Sun owner News Group Newspapers was settled before trial, and he won damages in his legal battle against Mirror Group Newspapers.