Donald Jr. and Vanessa Trump have welcomed their fourth child.

The baby boy joins older sister Kai, 5, and brothers Donald Jr., 3, and one-year-old Tristan.

Donald Trump Jr. tweeted: “It’s a BOY!!! @MrsVanessaTrump and baby are doing great.”

The businessman, who advises his father on The Apprentice, had earlier teased: “I actually never really got to bed. More on that later.”

And he joked that his son would soon be joining the family business, saying he’d be in the boardroom in “2 maybe 3 weeks;)”.

Donald Jr. and Vanessa Trump had taken their oldest two children to the Disney premiere of Secret Of The Wings in New York on Saturday.

Donald Jr. and Vanessa Trump have welcomed their fourth child

Vanessa Trump huge bump could clearly be seen as she posed in her black maxi dress.

On her return home Vanessa Trump joked she was lucky she hadn’t gone into labor.

“Made it back home! I’m so thankful I didn’t go into labor!,” she wrote.

“He’s very lucky! We are counting the days till we meet the little 1!”

The newborn makes a fifth grandchild and third grandson for business magnate Donald Trump Senior.

His daughter, Ivanka Trump, welcomed a daughter Arabella last year.

Donald Jr. and Vanessa Trump only welcomed their third child in October last year, with Vanessa conceiving again just three months later.

Vanessa Trump had been keeping her Twitter fans updated about the pregnancy’s progress, tweeting this week: “So I would love to hear what people think I’m having a boy or a girl?

“We won’t know till the little one is born but let’s see who’s right!”