The 'Stitches' hitmaker sparked speculation he was dating the 21-year-old model when they walked the Met Gala red carpet holding hands earlier this year, but they insisted they were just friends and she subsequently rekindled her romance with the 'Love Yourself' singer.
Hailey and Justin recently got engaged and Shawn thinks they are ''very good'' for each another.
He said: ''I found out [about the engagement] when everyone else did.
''And I'm so happy for them. Hailey and I are great friends. I'm also friends with Bieber. I think they're both actually very good for each other. It's crazy, though, it's a big thing.''
The 20-year-old pop star is currently single and admitted he is open to dating one of his fans because he doesn't think it would take them long to realise he's ''just a regular dude''.
He told the Sunday Times Style magazine: ''Sure, I'd date a fan. Why wouldn't you date someone who admires you? Isn't that what couples always say? 'She's my biggest fan.'
''The star shock only lasts a few hours. Then they realise I'm just a regular dude.''
Justin, 24, proposed to Hailey in July after a month of dating while vacationing in the Bahamas, and later confirmed the news in a heartfelt Instagram post in which he called his fiancée the ''love of his life''.
He wrote: ''Was gonna wait a while to say anything but word travels fast, listen plain and simple Hailey I am soooo in love with everything about you! So committed to spending my life getting to know every single part of you loving you patiently and kindLY. I promise to lead our family with honor and integrity letting Jesus through his Holy Spirit guide us in everything we do and every decision we make. My heart is COMPLETELY and FULLY YOURS and I will ALWAYS put you first! You are the love of my life Hailey Baldwin and I wouldn't want to spend it with anybody else. You make me so much better and we compliment eachother so well!! Can't wait for the best season of life yet!. (sic)''