The blonde babes were on hand at Palihouse in West Hollywood for a birthday party, but Brit actually came as a guest of her boyfriend Jason Trawick.
And it turns out Brit and P have more in common than their party past...They also share Brit's man! How so?
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Jason is Paris' agent and long-time friend.
And despite their rough patch right before Brit's birthday, the twosome seemed happier than ever. "You can tell that she and Jason are really in love," a source tells me, "He is a great guy and they make a great couple."
Britney, who wasn't drinking, stuck by Jason's side for the most part during the intimate 20-person party.
"Britney was shy with most of the people there. But she and Paris hugged and talked for awhile," the source says.
It was a big deal for the pop star to attend the low-key dinner, according to an insider.
"Britney hardly ever goes out so it was a major undertaking for her security," they tell me, "Her team came over yesterday afternoon and scoped it out to make sure everything was safe."
Clearly, Brit and Paris have calmed down since their wild times with Lindsay Lohan back in the day, as they both called it an early night. Brit departed with Jason. Paris, who'd been shooting her Oxygen series with Brooke Mueller and her sister Nicky at Palihouse before the party started, turned in before midnight.
Maybe this reformed twosome can get together with LL for game night soon?
PHOTOS: Hollywood party pics