However, a source close to the couple tells ET that the "Love Yourself" singer has been planning to propose for some time, and that they are "very excited about their future."
"Justin decided to propose to Hailey in front of a group of people in the Bahamas, but had been planning to ask her for a couple weeks now," the source says. "The ring is gorgeous and Hailey is over the moon with joy. The two can’t stop telling their friends and family how excited they are for their journey together. The two have always had a great bond, and it is stronger now than ever."
The pop star popped the question on Saturday night while they were staying at a resort in the Bahamas. The 24-year-old Bieber and 21-year-old Baldwin were spotted at a restaurant where everyone was salsa dancing, TMZ first reported. Unexpectedly, Bieber's security detail told everyone in attendance to put their phones away because "something special was about to happen," followed soon after by the singer's proposal.
"Justin got down on one knee and asked Hailey to marry him," the source tells ET. "Before he asked, he requested everyone watching respect their privacy and not take photos or video. Justin wanted it to be special."
The source adds, "Hailey was smiling for ear to ear and said, 'Yes!' The two then embraced and the crowd erupted with cheers."
ET has reached out to both Bieber and Baldwin's reps for comment.
The surprising proposal comes just days after the pair spent the weekend getting cozy and packing on the PDA in New York City, and jaunting around in the Hamptons. The two stars have not been shy about locking lips in the streets of the Big Apple since rekindling their romance over the last few months.
A source told ET late last month that the pair -- who originally dated in 2015, but split in early 2016 -- have been "casually dating for roughly a month" and that "things seem to be heating up as the two are spending more and more time together."