Eric Trump has said he is "sure" his sister Ivanka used her influence over their father to encourage the US president to launch military action against Bashar al-Assad in Syria.
Donald Trump ordered air strikes against a Syrian air base last Thursday night in response to a chemical weapons attack by the Assad regime on Tuesday that killed at least 87 people including more than 30 children.
“Ivanka is a mother of three kids and she has influence. I’m sure she said: ‘Listen, this is horrible stuff,’" Eric Trump told the Telegraph.
“My father will act in times like that. And by the way, he was anti doing anything with Syria two years ago. Then a leader gasses their own people, women and children. At some point America is the global leader and the world’s superpower has to come forward and act and they did with a lot of support of our allies and I think that’s a great thing.”
Although he emphasised he was not part of the White House administration, Eric Trump said he could tell his father was "deeply affected" by the images of injured children in the aftermath of the chemical weapons attack, in Idlib province, north-east Syria.
“I stay out of politics and I stay out of the administration but you can tell he was deeply affected by those images of the children," he said.
"There isn’t a single decent person in the world who saw those images and saw those kids being sprayed down by hoses to keep their skin from burning, who wasn’t deeply affected by what happened over there.
“It was horrible. These guys are savages and I’m glad he responded the way he responded.”
Ivanka Trump took on an official, unpaid role as Assistant to the President last month.
She has been a very visible presence during Mr Trump's first three months in the White House, focusing on policies relating to women and workforce development.
Ms Trump has participated in meetings with Shinzo Abe, the Japanese prime minister, Justin Trudeau, the Canadian prime minister and Angela Merkel, the German chancellor.
Her daughter Arabella, five, sang a Mandarin song for Xi Jinping, the Chinese president and his wife, Peng Liyuan, during a visit to Mr Trump's Mar-a-Lago resort last week.
Eric Trump, 33, who has taken over the running of his father’s property empire with his brother, Donald Jnr, said she has a positive influence over the president because she is never afraid to say 'no'.
"Ivanka is by his side in Washington. She is not involved in everything. I think she comes and goes with issues she deeply cares about but when you get to a certain level of power a lot of times, and you see this in business too, a lot of times people will say yes just because you happen to be the boss," he explained at the Trump Turnberry golf resort in Ayrshire.
“I think the beautiful thing about family is you play on a little bit of a different dynamic and once in a while you can pull them aside and say: ‘No disrespect but you might want to think about this or maybe you crossed the line here.’
“I think it gives you a sounding board who is a little bit more unconventional than the 37 people that might happen to be standing round a table at that one time who just want to appease.”
Ms Trump's husband, Jared Kushner, a special adviser to the president, was also believed to be firmly in favour of the US air strikes last week.
It is a position that reportedly put him at odds with Steve Bannon, Mr Trump's chief strategist, who did not apparently believe the action advanced Mr Trump's "America First" doctrine.
Mr Kushner and Mr Bannon have been locked in a "power struggle" within the White House, with Mr Trump calling on both of his senior aides to "work this out", according to reports.