Despite losing his case against the UK Home Office regarding police protection, Prince Harry carries on with his fight against the British press.

Amid a deepening Royal feud, the Prince has now involved his brother Prince William and Kate Middleton in his high profile case against Daily Mail.

New High Court filings revealed that the 41-year-old Duke of Sussex alleged that private investigators tracked and spied on his brother.

His legal team submitted documents that reportedly reveal surveillance around William’s 21st birthday party, along with phone records tied to the Princess of Wales’ maiden name.

Harry’s case against the Associated Newspapers risks heightening Royal Family tensions, with latest filings adding more fuel to the feud.

An invoice dated 2003 cites a payment for information surrounding Prince William’s Out of Africa themed 21st birthday party.

One document highlights mobile phone data connected to Catherine Middleton, now the Princess of Wales, while investigators seemingly also ran searches on her family home.

Another court document also mentioned a record of 10 numbers labeled “family and friends,” in which the 43-year-old Princess of Wales’ number stood out.

The High Court received the evidence on Wednesday, forming part of Prince Harry’s case against Associated Newspapers.

This development comes weeks after the Duke had a short reunion with his father King Charles at the Clarence House, after 19 months of being apart.

Harry joined six others in legal action against Associated Newspapers, claiming privacy breaches spanning 30 years.

The publisher, owner of the Mail on Sunday and MailOnline, denies the claims, calling them “lurid” and without basis.