US President Donald Trump’s younger brother Robert died  after being hospitalized for an unknown illness.

“It is with heavy heart I share that my wonderful brother, Robert, peacefully passed away tonight,” Mr Trump said in a White House statement.

“He was not just my brother, he was my best friend. He will be greatly missed, but we will meet again. His memory will live on in my heart forever. Robert, I love you. Rest in peace.”

The 74-year-old president had visited his brother on Friday at a hospital in New York, staying for about 45 minutes.

Media reports that Robert Trump was seriously ill, but there were no details of illness.

Donald Trump, who was stopping in New York on the way to his golf club in nearby Bedminster, New Jersey for the weekend, told reporters Friday only that “he’s having a hard time.”

While not famous than his older brother, Robert Trump, who was born in 1948, had an integral part of the family real estate empire and was loyal to the president.

Robert Trump unsuccessfully went to court to try to get an injunction preventing publication of a book by his niece Mary Trump, called ‘Too Much and Never Enough: How My Family Created the World’s Most Dangerous Man’.

The book, which paints Donald Trump as the product of a “toxic” family was a “disgrace,” Robert Trump said.

Although a temporary restraining order was applied, a judge lifted this in July, allowing publication.

Donald Trump has previously called his brother “wonderful” and said they have “had a great relationship for a long time, from day one.”

Donald Trump’s daughter Ivanka paid tribute to her uncle on Twitter.