The man who pioneered so-called gay cure therapy has died aged 70.

Dr. Joseph Nicolosi was co-founder of the National Association for Research & Therapy of Homosexuality (NARTH).

He became a prominent proponent of the therapy, which has been widely debunked by experts, and a major figure in the ‘ex-gay’ movement.

Dr. Nicolosi’s death was confirmed dead by the Thomas Aquinas Psychological Clinic, California, where he worked as clinical director.

The clinic announced the news on Facebook, writing: “We are deeply saddened and shocked to announce the death of Dr. Joseph Nicolosi yesterday in California from complications from the flu.”

He ran the clinic, the largest of its kind in the world, for more than three decades, writing four books on how to ‘cure’ homosexuality.

He claimed to run “the only secular group in the U.S. which protects the rights of therapists to counsel clients with unwanted homosexuality”, according to his website, which has more than 100,000 visitors every month.

In a documentary for Vice, Dr. Nicolosi explained how he believed he could ‘cure’ people of their same-sex attraction, claiming: “Everyone is homosexual. The idea that some people are naturally homosexual, or naturally gay, is a social construct.”

US Vice President has been an advocate of the debunked therapy in the past, though he has denied that since.

The pope has also criticised attempts to stop gay cure therapy, calling it an attack on ‘religious freedoms’.

On his website, Dr Nicolosi wrote that: “For many years, I have been assisting men and women –mostly, persons who are still at a crossroads about their sexual identity– to reduce their same-sex attractions and explore their heterosexual potential.

“I am a licensed clinical psychologist who shares your vision of humanity. I believe that our bodies tell us who we are, and that our bodies have made us for heterosexuality.

“Perhaps you experience same-sex attractions, but you believe you were not destined to be gay. You believe that these feelings do not represent ‘who you really are.’

“If this is your belief, then we may be able to help you.”

Therapy to change a person’s sexual orientation has been denounced by almost every major medical associations, including the American Medical Association, the American Psychiatric Association, and the American Psychological Association.

British medical bodies will strike off anyone who practices ‘gay cure’ therapy, though it isn’t illegal.