Two eyewitnesses claim the couple was at a resort Saturday night with a large group of people salsa dancing when Bieber's security detail urged everyone to lose their phones ahead of the special moment. "Excited for the next chapter!" - which fans believe is in response to the engagement news.
This time around, they have only been seeing each other for about a month - since Bieber and Selena Gomez tried and failed to get back together. On June 21, they pranked fans by sporting faux wedding bands when they knew they were being tailed by the paparazzi during an outing in New York City.
The post also included the Twitter handles of Bieber's parents, Jeremy Bieber and Pattie Mallette.
Meanwhile, Hailey was most recently linked to singer Shawn Mendes, but repeatedly denied claims of a romance.
Neither reps for Bieber nor Baldwin immediately responded to Fox News' request for comment.
In May she told the UK's "The Times" that she and Bieber, who both attend Hillsong Church in Los Angeles, had a tense time after their 2016 breakup. "I just don't want to hurt her". "He didn't wanna make it seem like Hailey really made him do it but I mean we all knew".
Hailey then said that after the break up the two "went through a long period of time when we weren't friends".