Baldwin, 21, and Bieber, 24, got engaged over the weekend in a shock announcement.
The model accepted his proposal during a Bahamas vacation with their friends in attendance.
And Baldwin was spotted sporting a huge diamond ring with two gold bands on her engagement finger on Sunday as the lovebirds celebrated at Nippers Bar & Grill in the Bahamas.
But in an interview back in May she revealed that Bieber had changed a lot from when the couple was first spotted kissing back in 2015.
She revealed: "He's somebody I really cherish. Now it's a very mature situation. It's good."
However, after the couple split they went through a difficult period where they did not talk.
She added: "I met him when I was really young and he was one of my best friends. Everybody knows that at a certain point in time that turned into something else, but that just happens when you're 18, 19.
"It was what it was. We went through a long period of time when we weren't friends. We didn't speak for quite some time and there was a lot of weirdness that went on. We've moved past that."
Another thing the couple has in common is religion.
They are both members of the Hillsong Church that was originally founded in Australia.
The church - which also boasts the Kardashians as members - has been criticized but Baldwin is keen to protect its reputation.
She added: "The thing about it being this celeb church is quite negative.
"But I think what they have done, in a good way, is make church approachable.
"People look at religion as a scary thing if they don't know what it's about. But at the end of the day, church is just a building; my personal beliefs are what matters."
Following the engagement news today her actor father, Stephen Baldwin, took to Twitter to congratulate the couple, before removing his Tweet.
Bieber's father Jeremy, posted a photo of Justin on Sunday with the caption: "@justinbieber proud is an understatement! Excited for the next chapter!"
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