Hayden Panettiere was found unresponsive in a living room armchair by her boyfriend's brother, TMZ has reported.
According to their anonymous source, Zach Hickerson found the actress in the chair at around 1.30pm on Sunday.
Brian Hickerson was asleep in a bedroom in the Greenville, South Carolina, loft where the pair had been staying, the source added.
Zach and Brian called 911 to alert when they failed to wake Hayden up. EMS teams 'worked on her' for nearly an hour before she was formally declared dead in front of the brothers, according to the police report.
An officer at the scene said Zach was 'very emotional' as he saw paramedics perform CPR. Brian did not appear to show emotion until Hayden was declared dead.
After cops arrived on the scene, Brian Hickerson allegedly then showed police a 'bag of medication' that Panettiere had been taking at the time of her death.
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 Hickerson was in the apartment where she died alongside his brother Zach (above together)
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The heavily redacted police report said officers arrived at 1.50pm, and officers found multiple EMS and firemen performing CPR for 'an extended amount of time' on the actress, 'who did not seem to have any obvious physical reasons to be unresponsive.'
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.
Panettiere first began dating Hickerson in 2018, however their on-off relationship became tumultuous as he was arrested several times on domestic violence charges.
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.
She had an 11-year-old daughter with her ex-partner Wladimir Klitschko, a former boxer turned Ukrainian government official who has full custody of the youngster.
In her memoir, titled This Is Me: A Reckoning, Panettiere alleged that Hickerson once 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, and described her relationship as a 'very dark and complicated time in my life.'
In one incident, Hickerson was arrested in May 2019, and court records show he was charged with injuring a spouse or girlfriend. He pleaded no contest to the allegations in April 2021, and he was sentenced to 45 days in county jail and four years' probation.
Just three days before Panettiere's death, Hickerson's request to reduce his past felony charges was denied by a judge.
Panettiere's relationship with Hickerson appeared to end in 2020, and in July of that year she filed for a restraining order against him. The outcome of her request is not stated in court records.
The Greenville Police Department said in a statement that 'the preliminary investigation has not indicated any signs of foul play or suspicious circumstances', and an autopsy found 'no signs of trauma were discovered that would have contributed to the death.'
Panettiere died in the Judson Mill Lofts apartment complex in Greenville, South Carolina, where she was temporarily staying
Panettiere died aged 36 on Sunday after suffering a suspected cardiac arrest
Panettiere had an 11-year-old daughter called Kaya following a life-threatening birth, but later gave full custody to her former fiancé, Ukrainian boxer Wladimir Klitschko
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Panettiere had an 11-year-old daughter called Kaya following a life-threatening birth, but later gave full custody to her former fiancé, Ukrainian boxer Wladimir Klitschko.
The star began acting as a child, appearing in soap operas, then gained wider recognition for her role in the 2000 sports drama Remember the Titans with Denzel Washington, and as the voice of Dot in Pixar's 1998 film A Bug's Life.
Panettiere later found fame playing cheerleader Claire Bennet in the superhero drama Heroes before starring as country singer Juliette Barnes for six seasons on Nashville.
She earned two Golden Globe nominations for best supporting actress on the show, while her singing produced 11 entries on the US Billboard Hot Country Songs charts.
Panettiere's film credits include 2006's Bring It On: All or Nothing, the comedy-drama film Raising Helen, and appearances in Scream 4 and Scream VI as Kirby Reed.