The Terminator star and former Governor of California attended the Vatican's General Audience and was able to greet the pope personally.

The 69-year-old is in Italy promoting his non-governmental organisation, R20 - Regions of Climate Action, which helps governments around the globe develop low carbon projects. During his brief meeting with the religious leader, Arnold spoke about his work with the organisation.

"It was my great, great honor to meet His Holiness Pope Francis," Arnold writes on "I am a huge fan - he is not only a wonderful leader for the Catholic Church, he is a fantastic steward for all of God's creatures. His environmental work inspires me and I look forward to working together for a clean energy future."

Arnold has been a strong advocate for climate change initiatives and, as California's Governor, he signed a bill creating America's first cap on greenhouse gas emissions.

The actor won't back down on his stance and has previously made it clear he couldn't care less if critics disagree with him.

"First - do you believe it is acceptable that 7 million people die every year from pollution?" he wrote in a Facebook post, titled, I don't give a f**k if we agree about climate change, in 2015. "That's more than murders, suicides, and car accidents - combined. My second question: do you believe coal and oil will be the fuels of the future?"

Aside from his political and environmental work, Arnold recently took over as the host of The New Celebrity Apprentice. Newly-elected U.S. President Donald Trump previously fronted the reality programme.