Thunberg has become increasingly prolific in recent months, after encouraging students globally to attend demonstrations demanding political action on climate change while 'on strike' from school. In addition, she has been nominated for a Nobel Peace Prize, as well as becoming the first recipient of the prestigious Prix Liberté.
She met Arnold Schwarzenegger at the launch of Austrian World Summit R20, his climate action organization advocating to speed up the implementation of the Paris Climate Agreement. This year's event was the third outing for the conference, which brings together politicians, experts, and prominent figures to exchange ideas.
Tweeting about the meeting, Schwarzenegger said: "Excited to kick off our @R20_AWS in Vienna. I have to admit I was starstruck when I met @gretathunberg. Tune in tomorrow."
Thunberg retweeted Schwarzenegger's words, adding: "Great to meet you too! We'll be back. Tomorrow."
The pair will join together this afternoon at the 'Climate Kirtag', a climate event at Vienna's Heldenplatz, bringing together speakers and interested members of the public. Thunberg and Schwarzenegger will speak, as well as others including ormer ski racer Aksel Lund Svindal.
Schwarzenegger talks about meat and the environment
Arnold Schwarzenegger, diet, and climate
Schwarzenegger has said in the past that he doesn't think he will ever be vegan, however, it is understood that he hasn't consumed dairy for many years. In addition, he has spoken out about 'feeling fantastic' while 'coming off meat'.
The star posted a video in 2017 discussing the impact of animal agriculture on greenhouse gas emissions, saying: "From an environmental point of view we know that raising livestock creates 28 percent of our greenhouse gases in the world.
"We have to reduce our greenhouse gases because we're killing seven million people a year because of our pollution. We can do better than that. Each and every one of us has the power to cut our consumption of meat. I just think we should all work together to reduce our pollution - I think this is a very important issue."