Justin Bieber I'm Getting a New Baby Sister! ... Dad's Wife is Preggo!

2/21/2018 12:21 PM PST

Justin Bieber is Getting a New Baby Sister

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There's a new Bieber coming into the world -- and it's a she ... TMZ has learned. 

Sources close to Justin Bieber's dad, Jeremy, tell us his new bride, Chelsey Rebelo, is pregnant with a baby girl -- which means Justin has a new sister on the way.

We're told Chelsey is about 16-20 weeks along (4-5 months) and that her and Jeremy's pink-themed wedding in Jamaica this week was in honor of their forthcoming daughter. It's her first kid with Jeremy -- who already has 3 of his own ... Justin, Jaxon and Jazmyn.

As we reported ... Justin didn't make a toast at his dad's wedding, but was pretty preoccupied with Selena Gomez during the trip. They were seen all day hugging and kissing. He also seemed to be in very good spirits, and now we fully know why.

Congrats to the Biebers!