"I was sad, obviously," Costner told PEOPLE about hearing the news that Brown, like her mother, was found unconscious in a tub on Saturday. "That family's under a lot of stress right now, just an enormous amount of stress."
After Nick Gordon discovered Brown, 21, and performed CPR until police arrived, she was immediately rushed to a hospital in Georgia. She is now surrounded by family and fighting for her life as sources say it will take a miracle for her to recover.
"I can't imagine," added Costner, 60, shaking his head with disbelief, before receiving a career achievement award at the 14th Annual AARP Movies for Grownups in Los Angeles on Monday.
Though Costner, currently starring in Black or White, admitted he hasn't spoken to Brown in "a little while," he wants nothing more than a speedy recovery for his former leading lady's daughter.
"I really hope she's okay," he said solemnly.
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