President Donald Trump on Friday is planning to visit his younger brother, Robert Trump, who is hospitalized in New York, a White House spokesman said.

Robert Trump, 71, is "very ill," according to ABC News, but his exact condition is unknown. The president will visit his brother's bedside en route to a preplanned weekend at his Bedminister, N.J., private golf resort.

The president has spoken fondly of his younger sibling, who is a fellow New York real estate executive.

"I have a wonderful brother and we've had a great relationship for a long time," Trump told reporters at the White House. He said he hoped that Robert would get better soon but that "he's having a hard time."

Robert Trump unsuccessfully sought to block publication this summer of his niece Mary Trump's best-selling tell-all book "Too Much and Never Enough" about their family.

Mary is the daughter of the oldest Trump sibling, Fred Trump Jr., who died in 1981 at the age of 43 after battling with alcohol addiction.

The Trump brothers also have two sisters, Maryanne Trump Barry and Elizabeth Trump Grau.

Robert Trump, like the president's other siblings, has mostly kept to himself during his brother's presidency, but said during the last campaign that he supported his brother "one thousand percent."

When Mary Trump's plan to write a book become public earlier this year, President Trump told Axios that his niece was "not allowed" to write the book, and his lawyer Charles Harder filed briefs on behalf of Robert, in an effort to block it. Robert Trump said in court papers that Mary Trump was prohibited from publishing such a memoir because she signed a confidentiality agreement in a 2001 inheritance case.

Mary described a family riven by a series of traumas, exacerbated by a daunting patriarch who "destroyed" Donald Trump by short-circuiting his "ability to develop and experience the entire spectrum of human emotion." The White House has said the book is full of falsehoods.

After the president's father Fred Trump Sr. died in 1999, there was an inheritance fight over what Fred Jr.'s family should receive.

During this time, Donald Trump relied especially on Robert, who served as a spokesman for the siblings in court documents. In fighting against the effort by Fred Trump III to gain support for his son with cerebral palsy, Robert Trump wrote that the family had provided financial support "out of the goodness of our hearts" and had given Fred III $200,000 annually even though they didn't have to lift "a finger" for the money.

The case was eventually settled and terms remain private.

While Robert Trump has often sided with Donald Trump in family disputes that have become public, he has had his own clashes with his brother, according to Jack O'Donnell, a former Atlantic City casino executive who worked with both men. In his memoir, "Trumped!," O'Donnell wrote that Donald Trump hired Robert to help run his casinos, which were then floundering. When Donald Trump complained during a meeting with his casino executives that "We're going to lose a fortune," Robert responded: "Donald, you know there's just no way to predict these things," according to O'Donnell.

Trump was furious with his brother, saying, "I'm sure as hell not going to listen to you in this situation. I listened to you and you got me into this," according to O'Donnell. Robert Trump said, "I'm getting out of here. I don't need this," O'Donnell wrote.

Donald Trump, in an interview for The Washington Post's biography, "Trump Revealed," said his brother "never quit" and did a "really good job."

O'Donnell said in a recent interview that Donald Trump promotes the "image of a strong loyal family," including his parents, children and siblings. Although O'Donnell said Robert gets along with Donald, he said he thinks the browbeating at the Taj Mahal casino "changed forever" their relationship.