Justin, 24, and Hailey, 21, were pictured last week attending a NY courthouse to apply for a marriage license - with reports claiming the couple actually got married soon after.
According to People, Hailey and Justin wanted to keep their nuptials top-secret, as the actual wedding hoopla is still to come.
"My sister was 24 when she got married, and my parents also got married when they were young, too", she told The Cut. "Well they went off and got married", he said casually.
Alec, who won an Emmy last fall for his Saturday Night Live impression of President Donald Trump, said he wasn't going to assume a protective role over Hailey toward Bieber, in their new nuptials. "And I don't know what the deal is".
A source told ET at the time that while Bieber and Baldwin did register for a marriage license, they did not have a marriage ceremony yet.
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In a since-deleted social media post, she wrote: "I understand where the speculation is coming from, but I'm not married yet!".
Justin popped the question to his model girlfriend two months ago, shortly after his split from on again/off again girlfriend Selena Gomez.
Metro.co.uk has contacted Justin and Hailey's reps for comment.
She responded with equally fulsome praise of her partner, telling him in a tweet: "Not sure what I did in life to deserve such happiness but I am so utterly grateful to God for giving me such an incredible person to share my life with!"
Hailey look totally on point, flashing her toned abs in a tiny crop top, PVC pants and denim jacket.