The pop star was recently heard referring to the model as his wife.
"The couple kept their marriage a secret from a lot of people. Justin and Hailey wanted to be married, and didn’t want to wait. They still plan to have a more formal wedding, but for them this intimate ceremony was exactly what they wanted.”
“Justin and Hailey were telling people they weren’t married when they were,” the source says, adding there are still plans for a wedding ceremony outside of the courthouse.
On Tuesday, TMZ was first to confirm the prior reports that the lovebirds tied the knot in New York City last month after they were spotted at the Marriage Bureau. While they are legally married, the pair have yet to have a wedding with family and friends, though they are already husband and wife.
TMZ further reported that the couple married without a prenup, and, despite them both reaching out to their lawyers, there's been no movement in drafting one.
Also this week, Bieber was heard referring to Baldwin as his wife when they visited the Stratford Perth Museum in Ontario, Canada, where there is an exhibit that centers around the "Sorry" singer's career.
“Justin very graciously introduced Hailey as his wife. Perhaps just a term of endearment? We loved their visit," the museum shared on Instagram along with a loving message that Baldwin left on the Belieber wall.
Back when rumors started swirling last month that the 24-year-old pop star was a married man, Baldwin took to Twitter in an attempt to put the rumors to rest, but she later deleted the tweet. "I understand where the speculation is coming from, but I’m not married yet!" she wrote.
"Justin and Hailey are still planning to have a wedding or celebration with their closest friends and family," another source told ET last month . "However, Justin is very spontaneous. [He] keeps Hailey and everyone on their toes."
Fans of Bieber also speculated that rumors of the marriage were true when his mother, Pattie Mallette, took to Twitter a few days after the couple were spotted at the government building. "Love is unconditional," she wrote.
The marriage news comes just a few months after Bieber proposed to the 21-year-old model while they were vacationing together in the Bahamas. The two were friends first, meeting nearly 10 years ago and briefly dating in 2015 and 2016. However, the feelings between Bieber and Baldwin "never really went away," according to a third source, which is why it wasn't alarming when they rekindled their romance this summer.
"Justin has always been in love with Hailey and is looking forward to being married," the source told ET earlier this month. "Justin has been in the spotlight for a long time, and his childhood was accelerated. After years of ups and downs, Justin took some time to evaluate everything in his life, took time off his tour [and] music and got to enjoy a more simple life."
"With that time, Justin knew he wanted to spend his time with Hailey and have a future with her," the source added.
Hear more on their whirlwind romance in the video below.