EXCLUSIVE

4/19 -- G Herbo was released from jail late Thursday night, and went on Instagram Live to talk about the altercation.

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Rapper G Herbo is facing a battery charge after an argument with his baby mama, Ariana Fletcher, allegedly turned physical ... TMZ has learned.

According to Atlanta Police ... the rapper and Ari got into it Wednesday morning -- mostly yelling at each other -- but at some point, cops say Herbo assaulted her. Cops say he then left the location with their son but later returned ... and after officers spoke to him, they arrested him for simple battery.

Cops say Ariana sustained minor scratches during the altercation, and right now it's unclear what triggered the alleged assault. Cops are continuing their investigation.

Perhaps complicating matters for G Herbo is the fact Ari is now dating boxer Gervonta Davis ... and is actually about 14 weeks pregnant with his child.

What's interesting is Ari and Gervonta were out partying Tuesday night at Allure Gentlemen's Club where G Herbo also happened to be. The trio was NOT there together. It's unclear if any encounter there might have led to the alleged assault the next morning.

Herbo is still in jail. His bond has been set at $2,000.