"It is with heavy heart I share that my wonderful brother, Robert, peacefully passed away tonight," the president said in a 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."
"Uncle Robert, we love you," Ivanka Trump tweeted Saturday night. "You are in our hearts and prayers, always."
President Trump had visited his brother Friday at New York-Presbyterian Hospital in Manhattan.
Robert Trump, who was three years younger than his brother, worked in corporate finance on Wall Street and later managed real estate holdings as a top executive for the Trump Organization.
The Millbrook, NY (Dutchess County) resident oversaw the organization's Atlantic City casinos as part of his duties as executive vice president.
He'd been married earlier this year to Ann Marie Pallan and was previously married to Blaine (Beard) Trump.
Robert Trump reportedly was hospitalized in serious condition in June with an undisclosed illness.
Roger Friedman of Showbiz411.com, citing sources, said he died of a stroke after battling heart disease.
"I have a wonderful brother. We have a great relationship for a long time, from day one," President Trump told reporters Friday afternoon. "Hopefully he'll be all right, (but) he's having a hard time."
Robert Trump is survived by two older sisters, Maryanne Barry, a retired federal judge, and Elizabeth Trump Grau, a former executive for Chase Manhattan Bank. He was predeceased by Fred Trump Jr.
No funeral plans were immediately announced. The president was expeced to attend.
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