The 39-year-old told Entertainment Tonight that: 'Although I only met her briefly, I wish her and her loved ones as much peace as possible and I'm so incredibly sorry for their loss.'
DREW BARRYMORE'S SISTER FOUND DEAD
JULIA ROBERTS AND FAMILY BLAMED IN SUICIDE NOTE
Drew's 47-year-old sister, with whom she shared a father, was found slumped behind the wheel of her car on Tuesday morning - just hours ahead of celebrating her birthday.
Police are currently treating the cause of death as 'unknown,' although pills were found scattered on the passenger seat of the vehicle, leading some to suspect that Jessica overdosed.
But Jessica's brother John revealed he believes his sibling died of drug misadventure, mixing alcohol with a cocktail of pills that resulted in accidental death.
'There were some empty vodka bottles, a couple of bags of meth and a variety of pills in the car. My guess is that it was the booze and pills, like with Heath Ledger,' he said.
Jessica had apparently visited her mother on the day of her death, before parking outside an apartment complex in San Diego, California at around midnight.
She was discovered the next morning by residents of the block who were trying to leave for work.
Drew had her own drug troubles as a teen, being admitted to rehab when she was just 13-years-old.
And it appears her half-sister Jessica also struggled with substance abuse, having also been in rehab in her youth.