Unless there is a sudden and staggering plot twist, Prince Harry’s legal battle against British tabloids for allegedly unlawfully intruding into his life reaches its most important moment on Tuesday when his claims against The Sun and the long-closed News of the World, come to trial.

The plot twist would be a settlement of his mammoth case against their parent, News Group Newspapers [NGN], the British press arm of the media empire founded by Rupert Murdoch.

Is it likely? You would get better odds on Harry and Megan announcing a weekly lifestyle column for The Sun on Sunday.

This will be the first time that News Group Newspapers has had to defend itself against allegations that its journalists and executives across the whole organisation were involved in or knew about unlawful newsgathering techniques.

If it were to lose, and lose badly, a finding from the court of corporate-level wrongdoing would be in stark contrast to a longstanding defence that phone hacking was limited to bad apples in one now-closed title.

The prince’s allegations of tabloid wrongdoing date back to 1996. Harry and his brother Prince William first became aware they may have been targeted in 2006.

Back then, texting was still in its infancy and everybody left voicemails – and some tabloid journalists realised it was rather easy to listen in.

Clive Goodman, a News of the World journalist, and Glenn Mulcaire, a private investigator, were arrested, and later jailed, for intercepting voicemails on phones belonging to the princes’ aides.

Prince Harry says as the scandal deepened, he held on for NGN to settle Royal Family claims under a “secret agreement” to avoid embarrassment in court. NGN’s lawyers have said this is “Alice in Wonderland stuff” – and the court has ruled it hasn’t seen evidence of such a backroom deal.

All these years on, the Duke of Sussex seems in no mood to give up on what has become a crusade against tabloid journalism. And so his case is going ahead – and what happens over the next two months may define both the prince’s legacy and the future of a British journalism institution.

NGN long ago apologised for unlawful practices at the News of the World and closed it down in 2011. It denies similar claims against The Sun – and the duke’s wider allegation of a corporate-wide cover-up.

It has settled cases brought by some 1,300 claimants, to the tune of around £1bn including legal costs.

That means it has seen off potential trials from people who say the newspapers ran stories that could have only been written with access to private or confidential sources of information that could not have been publicly known.

Those settlements left just two claimants – one of them Prince Harry.

When he launched his claim, he alleged that more than 200 articles published by NGN between 1996 and 2011 contained information gathered by illegal means. The trial will look at a sample of around 30 stories in detail.

Some of those will cover ground trodden in his successful Mirror Group case in 2023 and, just like in that case, he will give evidence in person.

There will be hours of analysis of how the Sun got scoops such as “Emotional Harry rang Chelsy at midnight” – a story it ran almost ten years ago to the day about his then girlfriend, Chelsy Davy.

There will be further separate allegations from the second claimant, Lord (Tom) Watson. The former Labour MP says his phone was targeted around the time he was investigating the Murdoch newspapers at the height of the scandal almost 15 years ago.

Mr Justice Fancourt will decide if any of the NGN articles were the product of unlawful information gathering, such as information tricked or “blagged” out of phone companies by private investigators.

In Prince Harry’s case, he will not rule on whether there was any phone hacking because Prince Harry ran out of legal time to bring those allegations to trial.

None of this is going to be simple in court.

The judge had repeatedly expressed his frustration, referring to the two sides as entrenched well-resourced armies refusing to give any ground to each other.

And at no stage has Prince Harry looked like he was going to settle, despite the enormous financial hit he faces by not doing so.

If a claimant turns down an offer of settlement and is later awarded less in damages by a judge, they have to pay the legal costs of both sides.

Prince Harry has been very open about the hit he will take and why he was pressing ahead.

“The goal is accountability. It’s really that simple,” he told an audience at a New York Times event in December.

News Group has, in simple terms, three lines of defence. It will firstly argue that Harry has run out of time to bring allegations of unlawful information gathering.

This saw off his mobile phone hacking claim.

Secondly, its lawyers will test, article-by-article, the duke’s claims that the information in them came from dodgy sources.

Thirdly, News Group has lined up witnesses to rebut Prince Harry and Lord Watson’s broader allegation that the top brass knew what was going on and were party to the mass destruction of purportedly incriminating records in 2011.

While the celebrity focus will inevitably be on the prince when he goes into the witness box, that third allegation of a cover up is the most important element of this trial.

While the hit to Prince Harry’s wallet will be big, the damage to NGN’s reputation – and that of its executives – would be greater still if the court finds they were involved.

The executives the claimants will accuse of wrongdoing include the current CEO, Rebekah Brooks. She was found not guilty of conspiracy to hack voicemails in the seismic 2014 trial that ended with the jailing of Andy Coulson, her former colleague, News of the World editor and David Cameron’s communications chief.

Another is Will Lewis. He played a key role in managing the hacking crisis in 2011. He is now the CEO of the Washington Post – an appointment that has been opposed by many at the newspaper because of this association.

They and others deny wrongdoing.

Will they be giving evidence? A spokesperson for NGN said: “Both claimants allege unlawful destruction of emails by News International between 2010-2011. This allegation is wrong, unsustainable, and is strongly denied. NGN will be calling a number of witnesses including technologists, lawyers and senior staff to defeat the claim.”

Exactly what evidence Prince Harry brings to prove this claim – and what NGN says in defence – may define the entire battle.

Tuesday really is the beginning of the end. And someone is going to lose – and lose big.