Robert Trump, the younger brother of the US president, has died aged 72, the White House has confirmed, APA reports citing BBC.
"He was not just my brother, he was my best friend," Donald Trump said in a statement on Saturday.
The president had visited his brother in hospital in New York on Friday afternoon, telling reporters: "He's having a hard time."
US media reports had said Robert Trump was seriously ill, but it is unclear what he was suffering from.
"It is with [a] heavy heart I share that my wonderful brother, Robert, peacefully passed away tonight," the president said. "His memory will live on in my heart forever."
Robert Trump was the youngest of the five Trump siblings, born two years after Donald.
He spent much of his career with the family real-estate firm, becoming a top executive. Unlike his brother, however, he was said not to court publicity and lived semi-retired in New York state.
He recently went to court in a failed bid to stop publication of his niece Mary Trump's tell-all book about the president, How My Family Created the World's Most Dangerous Man.
According to the New York Post, Robert spent more than a week in the intensive-care unit of Manhattan's Mount Sinai Hospital in June.