Now, Hilton is speaking out in support of the 38-year-old Spears, who reportedly campaigned in court for her father, Jamie, to not be reinstated as her sole conservator after he briefly stepped down.
"It breaks my heart that people have so much control over her," Hilton, 39, told The Sunday Times.
The former "Simple Life" star added: "It's not fair to be an adult and be treated like a child. I can't imagine having to live my life like that."
Last week, Spears' lawyer reportedly filed documents stating that the pop star was "strongly opposed" to her father returning as her sole conservator. The documents also reportedly stated that Spears' would prefer her care manager, Jodi Montgomery, “continue in that role as [she] has done for nearly a year" after Jamie stepped down after a bout of health complications.
The conservatorship was put in place in 2008 following the singer's public meltdown.
The court originally named Jamie Spears as the permanent conservator of her person, while her attorney, Andrew Wallet, was named the permanent co-conservator of her estate, according to People magazine. Per the outlet, Wallet exited his role last year.
The conservatorship is one of the reasons fans have launched the #FreeBritney campaign in an effort to show support for the songstress.
Hilton's support for Spears comes on the tail of her own allegations of abuse while at a Utah boarding school.
“The staff would say terrible things. They were constantly making me feel bad about myself and bully me," the heiress told People magazine. "I think it was their goal to break us down. And they were physically abusive, hitting and strangling us. They wanted to instill fear in the kids so we’d be too scared to disobey them.”
Education was not "at all" a focus of the institution, she alleged.
"From the moment I woke up until I went to bed, it was all day screaming in my face, yelling at me, continuous torture," Hilton further alleged.
Fox News' Melisa Roberto contributed to this report