The Bridegroom P.J. Mongelli told CNN that Trump was in the cocktail hour for the first time to meet the bride Nicole Marie and other family members. Mongelli said they had sent Trump several invitations, but did not know if he would actually turn up.
"It was a complete surprise," said Mongelli.
Mongelli said he asked the President for a favor – to greet the guests at the reception.
The video posted on social media showed Trump, wearing a dark suit but no tie, standing in a doorway, waving to the cheering crowd. The president gestured to the newly married couple of Staten Island to approach him, and they lined up beside him, pumping their fists and singing "USA! USA!" the video showed.
"He was such a gentleman," Mongelli said. "He was an ace."
Mongelli said he and his wife are both strong Trump supporters, as are most wedding guests. The couple got engaged in the golf club in November 201
The president spent the weekend at the Trump National Golf Club in Bedminster and returned to Washington on Sunday.
"I told the Japanese PM: I said," Come on, Shinzo, let's go over and say hello, "said Trump to the crowd at the wedding.