Maybe Bieber's woman wanted a clean-shaven look!

X17online can report exclusively that Selena Gomez spent the night at Bieber's new Hollywood Hills mansion last night, and X17 photographers spotted her leaving the pop star's new rental home around 10:30am on Thursday. Our photographer on the scene tells us, "Selena had her head down as she walked to her car; she was totally trying to sneak out. For some reason she and Justin don't want people to know they're back together."

Last night Bieber also posted an Instagram video of himself shaving his mustache and chin stubble, so it seems like Selena was sick of feeling that fuzz on his face every time they made out! Either way, these two are definitely back together, and though they didn't post any lovey dovey selfies from their sexy sleepover, given how much they've been hanging out lately, it's only a matter of time...

On Sunday Biebs drove Selena to her Tarzana home in his red Ferrari after the two spent the night together on Saturday.

Beliebers speculated the two were together at Bible study last week but other than an Instagram pic Justin deleted, neither has given any hints about their reunion...