University friends have described him as a caring and knowledgeable doctor who had some oddball tendencies.

Among one of the brightest in his class, Dr Bornstein was also known for his enthusiasm for writing epic poetry. He wrote his poems under the name Count Harold.

“He had long hair. He was irreverent. He sat mostly near the back of the room - where most of us did - and paid varying degrees of attention to what was being said at the time,” classmate Dr Edward Hurwitz told Stat News.

“He wrote strange poetry and gave [it] out to people,” Dr Hurwitz added.

According to a former patient, Dr Bornstein was a very good doctor but could also be "very moody".

“If he’s in a bad mood, you don’t want to talk to him,” according to Glen Edelstein. “He’s grouchy and argumentative. Sometimes he’ll get distant, staring at his computer and forgetting you’re sitting in the office with him.”

Why has he spoken about the letter now?

Dr Bornstein reportedly had a photograph of himself and Mr Trump in his office - but the president chose not to bring his personal doctor to the White House with him.

Mr Trump opted instead to keep on Ronny Jackson, President Barack Obama's White House doctor.