The Duke of Sussex, Prince Harry, continues to create ripples in the royal family as he takes the stand in his legal battle against the Mirror Group Newspapers.

This week, Harry testified at the High Court in London, unveiling the distress caused by the tabloid's coverage. Post his court appearance, an insider and royal analyst, Katie Nicholl, divulged that his father and brother are on edge, uncertain about what revelations Harry might make.

"I've been informed that both [King Charles III] and [Prince William] were quite apprehensive about Harry stepping into the witness box," shared Nicholl. "Given what emerged from Harry's evidence and his witness statement, their concern is understandable."

In his written evidence, Harry addressed the widespread speculation concerning his paternity, instigated by various media outlets. These stories purported that Harry's biological father was Major James Hewitt, Princess Diana's ex-lover, rather than Charles.

"Several newspapers had propagated a theory that James Hewitt, with whom my mother began a relationship after my birth, was actually my biological father," said the Duke. "When these articles, and others similar, were published, I was oblivious that my mother hadn't met Major Hewitt until after I had been born."

He also hinted at potential phone tapping by the tabloid, remembering instances where voicemails disappeared. "I recall instances of listening to a voicemail for the first time that wasn't fresh – I would attribute it to a technical error... or even my own forgetfulness due to heavy drinking the previous night," Harry added. "I distinctly remember people asking, 'Did you not get my voicemail?' I would search for it in my voicemail, but never found it."

Nicholl warned that as the trial progresses, Harry could disclose "details that the royal family would rather keep under wraps."

As previously reported by OK!, Nicholl isn't the first expert to voice concerns about Harry's potential revelations.

"His family is quite frightened," an insider said regarding Harry's impending statements. "There's a heightened level of anxiety about what Harry could disclose. His book was troubling enough."

The source referenced Harry's allegations that Charles and Camilla traded stories about Harry and Meghan Markle for positive coverage of themselves.

"He might decide to further elaborate on the narrative, making accusations in court," the source stated. "Did the entire family collude to tarnish Harry and Meghan's image to deflect attention from themselves?"

"Harry is having his day in court, and it's a day the royal family is not eagerly anticipating," the insider concluded. "They are all extremely apprehensive about what he'll disclose."

Nicholl's comments were reported by ET.