For weeks, The Washington Post has been trying to prove Donald Trump right about something: The presumptive Republican nominee's claim that he has given millions of dollars to charity, directly out of his own pocket.

But proof has been hard to find. Public records show no gifts from Trump to his own namesake charity, the Donald J. Trump Foundation, since 2008. A canvass of 200-plus charities, all of them with connections to the mogul, turned up just one small gift of less than $10,000 between 2009 and this May (when Trump, under pressure, made good on a $1 million pledge he had made to help veterans).

Then: a tip. DonorSearch, a professional search firm, had turned up a record that "Donald Trump" had given to the Roswell Park Alliance Foundation, which supports a cancer center in Buffalo.

The tip was right.

But the Trump was wrong.

"It’s trite, I know, but the way that I have done is my way of paying back for the benefits I have had … and hoping to facilitate others' experiencing the same benefit," said Donald L. "Skip" Trump, an oncologist specializing in genitourinary cancers, who served for several years as the Buffalo center's president and chief executive.

In looking for the presidential candidate's charity, I had found the doctor's giving by mistake.

Skip Trump said he had given about $120,000 to charity over the past five years. He had given his own money to the hospitals he had worked for, including Roswell Park and the University of Pittsburgh Medical Center; given to his alma mater, Johns Hopkins University; and given to his children's schools. "I sort of give what feels right. And I’ve been lucky to have some money that I can give," he said.

And Skip Trump had his own story about what it's like to get a donation out of the more famous Donald Trump. It turns out that it's difficult —  even if you share a name.

The first time Donald Trump was asked to give Donald Trump money, he didn't.

"A patient of mine actually wrote him a letter when I became CEO at Roswell Park, suggesting that he might seriously want to give money," Skip Trump recalled. That was about 2007. "I got a nice letter back from him, in response to my patient’s request."

But no money.

The next try was in 2010. This time, the more famous Donald Trump reached out to him.

"He called me, seeking to get the son of a friend of his access to a clinical trial that my colleagues at Roswell Park were running," Skip Trump said. As it turned out, his colleagues had already heard of this patient and were including him in the trial.

But while Skip Trump had the mogul on the phone, he took the opportunity to ask him for money. At that time, the cancer center was doing a "Bald for Bucks" fundraiser, in which staff members shaved their heads in return for donations.

"I suggested to Mr. Trump that maybe he should join me and shave his head. And he demurred at that opportunity," Skip Trump said. But, he said, the mogul made a video to help the cause and gave a donation. Although Skip Trump did not know it, the money did not come from Donald Trump himself: Tax records show the $30,000 came from his Donald J. Trump Foundation, a nonprofit organization largely stocked with other people's money. An official at Roswell Park said that the famous Donald Trump has never given the institution a personal gift of his own money.

After that 2010 gift, the mogul never gave to the cancer institute again.

"It would have been nice," said Skip Trump, but he hadn't expected any more.

Skip Trump is now chief executive of the Inova Schar Cancer Institute in Northern Virginia.

Would he ever hit the other Donald Trump up for a donation again?

"Absolutely," he said. "I’d love, maybe after November, when he’s looking for things to do —  maybe I’ll have the chance to connect with him again."