Justin Bieber and Jennifer Aniston made international headlines this week when they got new looks. Now the hairstylists behind the makeovers are revealing details behind the new 'dos.

"It was just time for a change," Aniston's longtime stylist Chris McMillan told Allure.com of the star's shorter look. "We had a blast doing it. And we've always liked this haircut. It's about keeping things simple. All the styles are back to when I first started doing hair. And I love it."

McMillian said it's all about the bob, and he has a very specific reason why. "I'm loving bobs again. It's a sexy look ... The reason that I'm loving a bob at the moment ... There are so many long, layered hairstyles and -- don't get me wrong, I love that. But 'The Real Housewives of Beverly Hills' all have that. You know what I mean? And what's the opposite direction you can go in?"