Country Star Brantley Gilbert's Wife Gives Birth in Tour Bus Mid-Show

Brantley Gilbert 's son seems born to be a rockstar ... 'cause his mom gave birth to him in his dad's tour bus mid-show -- before Gilbert ran back onstage and finished the show.

The country singer-songwriter posted a video to his Instagram from his show in Tupelo, Mississippi Friday night ... revealing he went out to perform his show before leaving the stage due to an some sort of emergency.

The camera follows BG offstage ... and, into his tour bus, where it shows his wife, Amber , holding their new baby boy -- apparently having given birth inside the bus.

Gilbert immediately calls his mom to tell her the good news ... lauding praise on his wife before telling Mama Gilbert he's gotta go finish the show -- and, getting back onstage to thousands of cheering fans.

BRANTLEY AND AMBER TOGETHER

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He raises his arms in triumph once reaching the mic ... telling them all that "We got a baby!" The rest of the video shows still images of the baby and other members of the band congratulating him.

Brantley and Amber announced back in May they were expecting another child ... posting the news on Mother's Day of this year while holding the sonogram.

The pair share three children: six-year-old Barrett , five-year-old Braylen , and the newborn whose name the couple has not yet shared.

Anyway ... congrats Gilbert family -- and, better buy that future musician a guitar ASAP!!!