LONDON -- Renowned theoretical physicist Stephen Hawking may have a good grasp of the workings of the universe, but he says he can't understand Donald Trump's popularity.

Hawking tells ITV's "Good Morning Britain" show that he has no explanation for the success of the presumptive Republican Party presidential nominee.

In a prerecorded interview set to air Tuesday, Hawking says Trump "is a demagogue who seems to appeal to the lowest common denominator."

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Hawking has a form of amyotrophic lateral sclerosis, known as Lou Gehrig's disease, that has gradually paralyzed him since he was first diagnosed at age 21.

Hawking, who speaks through a computer system operated with his cheek, also made a plea for British voters to choose to remain in the European Union in the June 23 referendum. He said it is important not only for economic and security research but also to further scientific research.

Meanwhile, Trump is expected to provide a full accounting of the Trump Foundation's donations to veterans' groups on Tuesday.

He told a Washington rally that an announcement about the donations would be made Tuesday, after telling reporters in North Dakota last week that there would be a news conference Tuesday morning. The presumptive GOP nominee is expected to clear up how much the campaign raised in January at a veterans' fundraiser it organized when he skipped a GOP presidential debate.

After the Washington Post pressed Trump to clarify how much has been given to veterans' groups from that event, the billionaire businessman fulfilled his promise to give $1 million of his own money to a charity for veterans.

Trump could announce gifts Tuesday to up to two dozen charities -- some of them have already received the donations, the report said.

Republican U.S. presidential candidate Donald Trump addresses the Rolling Thunder motorcycle rally to highlight POW-MIA issues on Memorial Day weekend in Washington, U.S. May 29, 2016. REUTERS/Jonathan Ernst

Last week, Trump's campaign manager Corey Lewandowski told "CBS This Morning" that Trump will give $5.5 to $6 million to veterans groups. At the January fundraiser, Trump claimed that the event had raised $6 million.

"We just cracked $6 million, right? Six million," Trump said at the time.

Lewandowski told CBS News that $4.5 million had already been "attributed" and that the total amount going to veterans' groups will be "somewhere between $5.5 and $6 million total, which would be given to the veterans."

He also said that the remainder would be distributed to groups by Memorial Day.