The row is the latest skirmish in a much wider battle between those who support Pope Francis and conservatives who are bitterly opposed to his populist touch and reform agenda, some of whom have gone as far as to accuse him of heresy.

They have been incensed by his suggestion that divorcees who remarry in civil ceremonies should be allowed to take Holy Communion.

Mr Sire, who has been a knight since 2001, was contracted to write a history of the order and lived from 2013 until 2017 in its palatial headquarters in Rome.

The book was duly published in 2016, but he then wrote a second book, without the knowledge of the knights, on Francis and his controversial papacy.

It was initially published under a pen name, Marcantonio Colonna, an Italian nobleman who fought at the Battle of Lepanto in 1571, in which a European naval force inflicted a major defeat on the Ottoman Empire off the coast of Greece.

Mr Sire, a Catholic arch-conservative who has questioned the liberalizing reforms of the Second Vatican Council in the 1960s, was revealed to be the author of the book earlier this week by his publishers.

After being unmasked, the knights took the decision to suspend him.

In a statement, the order said it “strongly condemns the vile attack against the Pope.”

“The Order of Malta dissociates itself from the positions conveyed and considers the content of the book a grave offence to His Holiness, Pope Francis.”

An internal investigation has been launched and Mr Sire could be expelled from the order, a spokesperson told The Telegraph.

In his book, Mr Sire also wrote about a damaging crisis within the order in 2016 which led to the downfall of its British head, Matthew Festing.

Mr Festing, a Cambridge-educated former Guards officer, resigned as the Prince and Grand Master of the knights in January last year after a highly public clash with the Holy See over his dismissal of a senior deputy.

He had accused Albrecht von Boeselager of condoning the distribution of condoms in an aid project in South-east Asia, in contravention of the Catholic order’s opposition to artificial contraception.

But after weeks of mud-slinging, which drew in the Vatican, German-born Mr von Boeselager, whose title is Grand Chancellor, was reinstated, in what was seen as a defeat for Mr Festing. He was then asked to step down by the Pope.

The row, which dragged on for months, tarnished the reputation of the Order, a Catholic charity which provides hospices, clinics and other relief for people in conflict zones and areas struck by natural disasters.

“Sire never had an official role in the order and he was not involved in any of the decision-making (during the crisis),” the spokesperson said.

The Dictator Pope was initially published as an e-book but a hard copy will be released on April 23, a week before the order meets in Rome to elect a new leader to replace the current acting head, Giacomo Dalla Torre del Tempio di Sanguinetto, an Italian academic.

He put out a statement claiming that his suspension was unlawful.

“The proceeding against me is wholly illegal,” he said, claiming that the way in which it was conducted breached the order’s own rules.

Founded in the 11th century to protect pilgrims travelling to the Holy Land, the Sovereign Military Hospitaller Order of St John of Jerusalem, of Rhodes and of Malta has around 25,000 paid employees and more than 80,000 volunteers around the world.

It is a sovereign entity which has observer status at the United Nations and maintains diplomatic links with more than 100 countries.