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Hayden Panettiere's on-off boyfriend Brian Hickerson and his brother were in the South Carolina apartment where the actress suffered a suspected fatal heart attack on Sunday, police say.

In a newly released report from the Greenville Police Department, officers said Hickerson and his brother Zach were at the scene when the Heroes star tragically died.

An officer at the scene said Zach was 'very emotional', but said Brian did not show any emotion as EMS declared his 36-year-old partner dead.

Brian Hickerson allegedly then showed police a 'bag of medication' that Panettiere had been taking at the time of her death.

The Greenville County Coroner’s Office has said Panettiere's cause of death remains under investigation, however audio of the 911 call from her apartment showed a dispatcher described it as a 'cardiac arrest.'

A dispatcher could be heard in the audio saying that Panettiere had suffered a suspected overdose, and sources told TMZ that Narcan - a nasal medication used to treat an opioid overdose - was also found on a mattress at the property.

An autopsy report completed on Monday found 'no signs of trauma were discovered that would have contributed to the death.'

Panettiere first began dating Hickerson in 2018, however their on-off relationship became tumultuous as he was arrested several times on domestic violence charges.

Hayden Panettiere's on-off boyfriend Brian Hickerson and his brother were in the South Carolina apartment where the actress suffered a fatal heart attack on Sunday, police say

Panettiere first began dating Hickerson in 2018, however their on-off relationship became tumultuous as he was arrested several times on domestic violence charges

The Heroes star's on-off boyfriend Brian Hickerson was in the apartment where she died alongside his brother Zach (seen together)

Panettiere had spoken of her troubled childhood in the spotlight in recent months, and revealed intimate details of her relationship with Hickerson in her memoir published three months before her death.

In her memoir, titled 'This Is Me: A Reckoning', Panettiere alleged that Hickerson beat her so severely that she had to remain in her house for weeks to keep her injuries from the public.

She said she tried to keep the alleged abuse from the police because she feared the public would find out.