The pop star shared a brief sneak peek at a recent getaway south of the border she was on -- or still be in the middle of -- Thursday by posting a video that shows her having a good time with her older bro ... and from the sounds of it, they might be knocking back drinks.

In the clip ... Britney can be seen filming a group of musicians, but then there's a jump cut of her standing next to Bryan in the middle of a town, and he says -- "Let's go to the bar."

There's another cut that shows Britney and Bryan inside some kind of rental, with Bryan walking around in an oversized coat that Britney compliments -- likening him to Elvis.

Later, we saw Bryan leaning over a table with a bunch of plates of food in front of him -- and Britney jokingly notes he must be famished. Her caption to this video reads, "After the bar with my brother !!! Well I guess he thought he was Elvis 🤷‍♀️🤷‍♀️🤷‍♀️🌷🌷🌷😂😂😂 !!!"

The trip has already proven to be quite eventful for Britney -- on Wednesday, she posted yet another video of herself down there, and her caption noted she got lost in the downtown of the Mexican town she's in for about an hour.

She added ... "It was horrific … but I found my way and I’m laying out now … it’s beautiful today."

This is the 2nd time Britney and Bryan have hung out in recent months -- despite being estranged from her other family members. Remember, Britney and her brother bonded while hitting up a Las Vegas spa together -- later linking up with her ex-fiancé, Jason Trawick.

Sources told us that Bryan and Jason have remained close after his split from Britney.

These days Britney has been romantically linked to Paul Soliz ... the ex-housekeeper who BS got into a heated fight with at the Chateau Marmont last month.

Earlier this spring, multiple sources told TMZ ... Britney's mental health has been in a tailspin following the end of her conservatorship ... with the star allegedly spending a lot on vacays and drinking instead of taking her meds.