Stephen Hawking, a theoretical physicist and cosmologist, said that presumptive GOP nominee Donald Trump is a demagogue. Hawking, a British citizen, has even acknowledged on Tuesday that he couldn’t find a viable explanation behind Trump’s rise to popularity.

“He is a demagogue who seems to appeal to the lowest common denominator,” he told ITV’s “Good Morning Britain” on Tuesday as quoted by the Washington Post. Hawking, who has been suffering from amyotrophic lateral sclerosis for decades, is not the first British personality to speak out against Trump. British Prime Minister David Cameron publicly criticized Trump’s call to ban Muslims from entering the US borders.

The newly elected London Mayor Sadiq Khan, who is a Muslim, said, “If Donald Trump becomes the president I’ll be stopped from going there by virtue of my faith, which means I can’t engage with American mayors and swap ideas.”

Trump’s ascent to power has been the subject of concern as well as of surprise to many. He has managed to secure the FOP nomination last week by reaching the required number of delegates. Hawking may have been able to explain a few baffling elements of the universe, but the phenomenon of Trump’s smooth march towards the GOP nomination seemed impenetrable for the brilliant mind to decode.

Stephen Hawking also expressed his opinion on Brexit during the interview. According to him, if Britain leaves the European Union, it would be catastrophic for science as the finances would be affected. Tighter immigration is also likely to have repercussions on research prospects.

“Gone are the days when we could stand on our own, against the world,” The New York Times quoted him as saying. “We need to be part of a larger group of nations, both for our security and our trade. The possibility of our leaving the EU has already led to a sharp fall in the pound, because the markets judge that it will damage our economy.”

A referendum on whether Britain will stay in the EU will be held on June 23. Those who favour Brexit argue that being a part of a bloc has diminished Britain’s influence and sovereignty.