A new book "In The Closet of the Vatican" claims the vast majority of priests are gay. (Vincenzo Pinto/AFP/Getty)

The vast majority of Vatican priests are gay, claims an explosive new book set for release on February 21.

French journalist and author Frédéric Martel, who is gay and has written various books about LGBT+ rights, carried out 1,500 interviews over four years for his new book, In the Closet of the Vatican.

The sources include 41 cardinals, 52 bishops and monsignors, 45 papal ambassadors or diplomatic officials, 11 Swiss guards and more than 200 priests and seminarians, the Catholic news outlet The Tablet reported.

“The refusal to acknowledge gay rights is based on hypocrisy.” — Frédéric Martel

According to Martel’s sources, as many as 80 percent of Vatican priests are gay, but not as many are sexually active.

The rule of thumb, reads the promotional material available on the book’s British publisher Bloomsbury, is that “the more a prelate is homophobic, the more likely it is that he is himself gay.”

Martel denounced the Vatican’s stance on homosexuality already in 2014, an interview with HuffPo Italy while promoting his book Global Gay: How Gay Culture Is Changing the World.

“The [Vatican’s] refusal to acknowledge gay rights is based on hypocrisy: many people within the Vatican are gay—a phenomenon that also derives from the imposition of celibacy—so as a reaction they show an excessing anti-gay behaviour,” he said.

“In short, the more you are gay in private, the more you will be homophobic in public. This is the Vatican’s secret.”

Vatican priests who are homophobic in public are secretly gay, book claims

Martel’s latest book set out to further explore and unveil this secret, with Bloomsbury describing the book as “a startling account of corruption and hypocrisy at the heart of the Vatican.”

One of the book’s most explosive claims, according to The Tablet, is that the late Colombian Cardinal Alfonso López Trujillo, a former President of the Pontifical Council for the Family and a staunch defender of the Catholic teachings on homosexuality and contraception, used to pay male escorts.

In the Closet of the Vatican is due to be published in 20 countries and eight languages on the same day that more than 100 bishops from across the world gather in Vatican City to hold a four-day summit discussing the scourge of sexual abuse.

According to The Tablet, the timing of In the Closet of the Vatican‘s publication raised concerns that the book may be used to blame sexual abuse on homosexuality—a connection that the book itself reportedly never makes, but something that several members of the clergy, most recently German cardinal Walter Brandmuller, have claimed.

Rather, the book points to the culture of secrecy that “starts in junior seminaries and continues right up to the Vatican itself” as creating a climate that makes it difficult to denounce clerical sex abuse.