Donald Trump to be a grandfather for the ninth time as Eric and Lara Trump announce they are expecting their first child

Donald Trump is to be a grandfather for the ninth time. Photo / AP

Eric and Lara Trump are expecting their first child, they have announced - a ninth grandchild for President Donald Trump.

The couple, who found out on Eric Trump's birthday in January, said the president was so thrilled by the news they were worried he would announce their news for them.

"Eric's dad was so excited," said Mrs Trump, 34. "We were worried he'd blurt it out at a press conference."

She told People magazine that she thought her 33-year-old husband would make a wonderful father. His older brother, Don Jr, has five children while his older sister, Ivanka, is a mother of three.

Eric and Lara Trump have announced they are expecting their first child. Photo / AP

"Eric's going to be an amazing dad," she said. "The nieces and nephews love hanging with him. He's the cool uncle. He's watched Frozen many times."

Mrs Trump, who worked as a personal trainer and model before moving into television producing, said that they were expecting a boy. They considered naming him Charlie - but that name has already been given to their dog.

"I was exhausted in the beginning," she said.

"It surprised me, because I'm a very active person, and until the fatigue hit, I didn't believe it would actually happen to me.

"It really affected me. But I'm feeling really good now."

The boy is due in September.

And the New York-based couple - Eric Trump is in charge of running the golf division of the Trump business - have made no secret of their wish to start a family.

"Maybe when this crazy political race is over, we'll start working on the kid thing," said Mr Trump, during the campaign.