Details have emerged of last month's "palace coup" in Saudi Arabia which saw the king's 31-year-old son depose his cousin to become heir to the throne.

Mohammed bin Nayef, the former crown prince, was reportedly held in a room in a royal palace in Mecca and told he could not leave until he surrendered his powers to his younger cousin, Mohammed bin Salman.

As part of the midnight plot, The New York Times reported, senior Saudi princes were told in a secret briefing that the 57-year-old bin Nayef's alleged addiction to painkillers rendered him unfit to become king.

The Saudi government has been at pains to show there are no hard feelings between the deposed bin Nayef and his younger cousin, but the new account of the royal manoeuvrings shows the transition was less amicable than presented.

Prince Mohammed bin Salman of Saudi Arabia credit: EPA

Bin Nayef, often known as MbN, was reportedly summoned to the Safa Palace on the evening of June 20 for what he thought was a regular meeting with King Salman bin Abdulaziz.

Instead, he was reportedly taken into a side room and stripped of his mobile phone by royal officials, who told him he needed to give up his role as crown prince and relinquish the powerful role of interior minister.

Bin Nayaf initially refused, according to the newspaper, but as the night dragged on towards sunrise he eventually gave in.

In 2009, bin Nayef narrowly survived an al-Qaeda assassination attempt. It has been rumoured that he began taking painkillers after the attack, and became addicted. Bin Nayef has not commented publicly on these claims.

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Bin Nayef was also reportedly opposed to the Saudi-led diplomatic campaign against its neighbour, Qatar, which may have hastened his demotion.

Saudi and its three allies said yesterday that they were no longer insisting Qatar meet a list of 13 demands, including closing the al-Jazeera TV network.

A senior Saudi official yesterday said the account of bin Nayef's demotion was "unfounded and untrue, in addition to being nonsense".

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The official said bin Nayef had been removed from his post in the national interest and had not experienced any "pressure or disrespect".

"The story depicted here is a complete fantasy worthy of Hollywood," the official said in a statement to Reuters.

Three royal insiders, four Arab officials with links to the ruling house of Saud, and diplomats in the region, told Reuters that MbN was surprised to be ordered to step aside.

"It was a big shock to MbN," said a Saudi political source close to MbN. "It was a coup. He wasn't prepared."