Hayden Panettiere's BF Brian Hickerson Bar Fight Triggered by Smack Talk on Her Death

Hayden Panettiere’s boyfriend Brian Hickerson was being heckled for the late actress’ death moments before his bar altercation that led to his brother Zach’s arrest, TMZ has learned.

Sources close to the brothers tell TMZ … Brian, who has lost around 40 pounds while grieving Hayden’s death, was encouraged to leave the house this weekend by his brother.

We’re told Zach wanted Brian to get out because he has been extremely heartbroken since Hayden’s death ... and convinced Brian to go out for a low-key night to watch the game at a local restaurant.

Our sources say the brothers even spent some time talking about Hayden during the evening ... but we're told the night took a disturbing turn when people at the restaurant allegedly began harassing the brothers.

We’re told someone in the bar told Brian, “You killed her. You probably beat her to death.”

As we previously reported, TMZ obtained video of the brothers in a heated exchange with some Greenville, South Carolina bar-goers.

Brian and Zach strongly deny any involvement in Hayden's death.

The confrontation over the weekend ultimately led to police being called. Cops told us Brian was detained but not arrested, while Zach was arrested on a disorderly conduct charge after police said he was highly intoxicated and yelling profanities in public.

The brothers' emotional reaction comes as the investigation into Hayden's death continues. Brian and Zach found Hayden unresponsive ... they have not been named as suspects and authorities have not charged either brother in connection with her death.

For Brian, we're told, the situation has been especially painful ... because he says he's not only dealing with the loss of Hayden, but also the public accusations surrounding it.