In fact, OK! can exclusively reveal that Jen paid her first ever overnight visit to John's L.A. bachelor pad on Thursday night.

Dressed casually in jeans and with her hair down as she rode in the back of her security detail's car, Jen arrived at John's home in Pacific Palisades around 9:30pm PT.

As she stepped out of the car and headed into the house, it looked like she was carrying an overnight bag. This small gesture marks a huge moment in their relationship.

"Since they started dating, they always — ALWAYS — stayed at Jen's place," an insider explains to OK!.

"John's home is your typical bachelor pad; it's run-down, overgrown with trees and needs a paint job. There's probably a moldy tuna fish sandwich and a six-pack of beer in the fridge. That's not exactly what Jen is used to."

Of course, this special visit from Jen comes on a special night for the singer, as he celebrates his 31st birthday.

Last night, the pair got an early start on the festivities by hitting the town to party at an exclusive cigar bar in L.A.

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