Following his brother's death, Trump paid his tributes.

"It is with [a] heavy heart I share that my wonderful brother, Robert, peacefully passed away tonight," the US President said in a statement.

"He was not just my brother, he was my best friend.

"His memory will live on in my heart forever," Trump said. 

Though it is unclear what caused Robert Trump's death, local media reports suggested he had been seriously ill and was admitted in a hospital in New York.

Robert was the youngest of Fred and Mary Anne Trump's five children and was born two years after Donald Trump.