Reason behind Justin Bieber's baby's name explained as he announces birth of first child

Justin and Hailey Bieber's baby name has been explained after the pair announced the birth of their first child.

The celebrity couple have been married for six years, and only announced that they were pregnant for the first time in May this year, the same time that they renewed their wedding vows in Hawaii.

When they revealed the news on social media, Hailey was already six months pregnant, as they shared videos and photos of the surprise news to their millions of followers online.

However, fans have had to wait with bated breath as the exact due date of their son was never revealed to the world.

Hailey has been sporting the baby bump in public for the past three months. (Gotham/GC Images)

But on Friday, Justin Bieber posted on his Instagram, joyfully announcing that their baby boy was born, posting a photo of wife Hailey holding their son's tiny foot.

The 30-year-old announced the boy's name in the caption of the post, writing: "WELCOME HOME JACK BLUES BIEBER."

The unique name was also shared by Hailey, 27, on her own Instagram account, as she reposted her husband's snap on her story, simply writing 'Jack Blues' towards the bottom, with a teddy bear and blue heart emoji.

Bieber's post has currently got more than eight and a half million likes, as well as thousands of comments, though a lot of mystery surrounds one aspect of their boy - his name.

The name Jack comes from Justin's father, Jeremy Bieber, whose middle name is Jack.

Jeremy separated from Justin's mother, Pattie Mallette, when they were both 18 and though Justin didn't see his dad much growing up, the pair have since made up and now have a positive relationship with one another, leading to the sentimental naming of his son after his father.

The couple announced the birth of their boy on Friday. (Instagram/Justin Bieber)

A source previously revealed to People that the 'Baby' singer was 'so excited' to become a dad, and also that the parents had chosen the 'perfect' name for their child ahead of time.

Hailey Bieber previously spoke to W Magazine in July, revealing how she hid her pregnancy from the public for six months.

"I was honestly able to keep it quiet because I stayed small for a long time. I didn't have a belly, really, until I was six months pregnant, which was when I announced it. I was able to wear big jackets and stuff," she explained.

"I probably could have hid it until the end. But I didn't enjoy the stress of not being able to enjoy my pregnancy outwardly."

She also said that it felt like she was 'hiding this big secret, and it didn't feel good. I wanted the freedom to go out and live my life.'