The Duchess of Sussex has begun legal action against the Mail on Sunday over a claim that it unlawfully published one of her private letters.
In a statement, the Duke of Sussex said he and Meghan were forced to take action against “relentless propaganda”.
Prince Harry said: “I lost my mother and now I watch my wife falling victim to the same powerful forces.”
A Mail on Sunday spokesman said the paper stood by the story it published and would defend the case “vigorously”.
Law firm Schillings, acting for the duchess, accused the paper of a campaign of false derogatory stories.
The firm has filed a High Court claim against the paper and its parent company over the alleged misuse of private information, infringement of copyright and breach of the Data Protection Act 2018.
The claim comes after the Mail on Sunday published a handwritten letter from Meghan to her father, Thomas Markle, sent shortly after she and Prince Harry got married in 2018.
In a lengthy personal statement on the Duke and Duchess of Sussex’s official website, Prince Harry said the “painful” impact of intrusive media coverage had driven the couple to take action.
Referring to his late mother Diana, Princess of Wales, the prince said his “deepest fear is history repeating itself”.
“I’ve seen what happens when someone I love is commoditised to the point that they are no longer treated or seen as a real person,” he said.
BBC royal correspondent Nicholas Witchell said the statement was “remarkably outspoken” and “nothing less than a stinging attack on the British tabloid media”.
Former Daily Mirror editor and Guardian columnist Roy Greenslade said the duchess could win the legal action, but added Prince Harry had taken a risk by attacking the press for the actions of one newspaper.
“The press – particularly the tabloid press – is far less powerful now than it was during his mother’s era,” he told Radio 4’s Today programme.
“Is he taking a sledgehammer to crack a nut here? I think he may well find that this is counter-productive.”