The upstate man accused of killing teenage social media star Bianca Devins and then posting grisly photos of her lifeless body on Instagram pleaded not guilty on Monday.

Brandon Clark, 21, had been charged with second-degree murder for allegedly slitting his 17-year-old girlfriend’s throat earlier this month.

Oneida County District Attorney Scott McNamara previously said Clark — who met Devins about two months ago on Instagram — flipped out when the influencer kissed another man at a Queens concert July 13.

Early the next morning, the couple drove back up to Utica, where Clark allegedly slit Devins’ throat with a large knife.

He then posted a photo of her bloody body to Instagram and called 911, prosecutors said.

When cops arrived, Clark cut his own throat, then posted a photo of his bleeding neck on the app.

On Monday, Devins’ friends and family filled the Oneida County courtroom where Clark, of Bridgewater, pleaded not guilty.

Clark’s lawyer, Luke Nebush, cited the ongoing investigations and said he wouldn’t discuss details of the case publicly.

With Post wires