In addition to the Mirror's parent company, Harry is also suing News Group Newspapers, The Sun, and Associated Newspapers Ltd, which owns the Daily Mail and Mail on Sunday.
As the Duke of Sussex gets ready to take the witness stand, the royal family is bracing themselves for the potential impact.
A highly placed source within the palace, cited by Page Six, revealed that Harry's estranged family is not pleased with the situation.
"It's hard to imagine anyone being pleased," the source said, further stating that they will be privately preparing themselves for what may come.
"Harry sees himself as fighting their battle too, in order to protect the monarchy's reputation," another insider stated. "However, the royal family generally avoids confrontation with the media, and litigation is a lengthy, stressful, unpredictable, and expensive process."
The source continued, "You just don't know which direction the other side will take or what they might bring up."
During the court proceedings, lawyer Andrew Green KC, representing Mirror Group Newspapers (MGN), claimed that the information used for many of the published stories was "disclosed by or on behalf of royal households or members of the royal family."
"There's a significant reason why the royal family should feel uneasy about this," the royal insider added.
Harry has already faced criticism from the judge for not appearing in court on the first day of the trial, as he was busy celebrating his daughter, Princess Lilibet's second birthday in California.
