Rupert Murdoch is locked in a secret legal battle against three of his children over the future of the family’s media empire, as he moves to preserve it as a conservative political force after his death, according to a sealed court document obtained by The New York Times.

Murdoch, 93, set the drama in motion late last year, when he made a surprise move to change the terms of the Murdochs’ irrevocable family trust to ensure that his eldest son and chosen successor, Lachlan, would remain in charge of his vast collection of television networks and newspapers.

The trust currently hands control of the family business to the four oldest children when Murdoch dies. But he is arguing in court that only by empowering Lachlan to run the company without interference from his more politically moderate siblings can he preserve its conservative editorial bent, and thus protect its commercial value for all his heirs.

Those three siblings — James, Elisabeth and Prudence — have united to stop their father. Lachlan has joined on Rupert Murdoch’s side.

Last month, the Nevada probate commissioner found that Murdoch could amend the trust if he is able to show he is acting in good faith and for the sole benefit of his heirs, according to a copy of his 48-page decision.

A trial to determine whether Murdoch is in fact acting in good faith is expected to start in September.

Hanging in the balance will be the future of one of the most politically influential media companies in the English-speaking world.

Representatives for the two sides declined to comment. Both have hired high-powered litigators.

The Murdoch family has been divided before. James and Elisabeth at one point competed with each other and Lachlan to eventually take over the company, and at various times they have clashed with one another and their father. James, who once helped run the company with Lachlan, left it in 2019.

But given Rupert Murdoch’s advanced age, this battle has all of the makings of a final fight for control of his sprawling media conglomerates, which own Fox News, The Wall Street Journal, the New York Post and major newspapers and television outlets in Australia and Britain.

Politics, and power, are at the root of the struggle. Since Murdoch designed the trust nearly 25 years ago, the family’s political views have diverged sharply.

During Donald J. Trump’s rise, Murdoch and Lachlan became more closely aligned, pushing the company’s most influential outlet, Fox News, further to the Right, making the other three children increasingly uncomfortable.