The "Total Recall" star, who had suffered a stroke in 2001, reveals she was going through her own undisclosed personal troubles at the time, and was unable to provide the support Spears so desperately needed after cutting off her signature long, blonde hair in 2007.
"Britney wrote to me a very long and important, poignant letter during a very difficult time in her life - about the time when people would recognise it, when she shaved her head - wanting me to help her," Stone explained on America's "The Kelly Clarkson Show", which aired on Wednesday (31Mar21).
"I was in a very difficult time of my life, and I couldn't help myself. But the truth of the matter is we both needed help. She needed help and I needed help."
Stone admits she can relate to Britney's conservatorship fight with her father, Jamie Spears, as she attempts to regain control of her own finances because the actress has also experienced similar money-related challenges in her career.
"The true fact of it is it's very hard to be a very successful woman and not have everyone controlling you, taking your finances and handling you," Stone said.
"I'm sure all of the young stars get handled, you get handled so much that there's a huge breaking point. There's a part where you get broken."
Branding Britney's situation "so out of control and awful," the actress added, "I can say certainly it's been very out of control and very awful more than once in my life and I have certainly had it. It's very complicated to take control of your life. It's very hard to get control of your finances."
It's unclear if Stone has since personally connected with the pop superstar, but Britney recently gave the Hollywood icon a shout out on Instagram as she highlighted the celebrity women who have "truly inspired" her throughout her life.
Stone's comments emerge a day after Britney confessed she broke down in tears following the release of the "Framing Britney Spears" documentary, which details her conservatorship battle and delves into her misogynistic media treatment during her rise to fame.
Addressing the New York Times film on Instagram, she wrote, "I didn't watch the documentary but from what I did see of it I was embarrassed by the light they put me in... I cried for two weeks and well.... I still cry sometimes (sic)!!!!"