It’s a real-life “Game of Thrones” in the desert kingdom.

Saudi Arabia’s Crown Prince Mohammad bin Salman tightened his grip on power Friday with the arrests of three top-ranking relatives — including the only surviving brother of his father, King Salman — who were once considered the prince’s rivals for the throne.

Prince Ahmed bin Abdulaziz al Saud and Prince Mohammed bin Nayef bin Abdulaziz al Saud, the king’s nephew, were taken into custody and accused of treason, sources told The Wall Street Journal — a capital crime in the kingdom. A royal cousin, Prince Nawaf bin Nayef, was also arrested.

The 35-year-old crown prince, known as MBS, has been the country’s de facto ruler since 2017, when his father ousted Mohammed bin Nayef, the former crown prince, in MBS’s favor.

MBS has won international praise for efforts to modernize the kingdom, such as abolishing rules that forbade women from driving.

But he has been ruthless in his pursuit of dominance within the royal family, arresting dozens of relatives on corruption charges in 2017 — and has been accused of ordering the gruesome death of Jamal Khashoggi, a critic of the regime, in 2018.