Donald Trump Jr. and his wife Vanessa Trump have welcomed their fourth child into the world.

"It's a BOY!!! [Vanessa] and baby are doing great," Trump Jr. tweeted Sunday.

The Celebrity Apprentice advisor also revealed via Twitter he and his wife had decided to name their new baby Spencer Frederick Trump -- Spencer because they "liked it" and Fred after his grandfather.

The couple had announced Vanessa was pregnant with baby no. 4 in early May.

Spencer Frederick joins siblings Kai Madison, a six-year-old daughter, who was born in May 2007; Donald Trump III, a three-year-old son whom Vanessa gave birth to in February 2009; and a one-year-old son named Tristan Milos Trump, who was born on October 2 of last year.

"Kai: dad I don't want any brothers, I want to be the only kid! Me: Ok I will find you a new family where you can be the only kid! Kai: GRRRR," Trump Jr. tweeted yesterday.

However, Kai Madison is now apparently looking forward to meeting her new little brother.

"Getting Spencer ready to go home for the first time. Kai Donnie and Tristan are very excited to see him," Trump Jr. tweeted on Tuesday.

Spencer Frederick is the fifth grandchild for Trump Jr.'s father, The Celebrity Apprentice star Donald Trump. 

Trump Jr.'s sister and fellow The Celebrity Apprentice advisor Ivanka Trump and her husband Jared Kushner have one child together, as they welcomed a baby girl into the world in July 2011.