Cara Delevingne is worried her mother will have a ''relapse''.

The 'Paper Towns' star's mother Pandora suffered from a heroin addiction in the past and the 22-year-old actress is reportedly terrified that her mother will find herself in a ''spiral of misfortune''.

A source told HollywoodLife.com: ''Every day is a struggle for Cara's mom, Pandora, in regards to her heroin addiction. She's clean at the moment and has had her good days and bad days, but as anyone with addiction problems will tell you, you have to take it one day at a time.

''You can never cure yourself of addiction, only control it. That's why Cara fears she's struggling because you don't know what the next day could bring. One event could change everything and lead to a spiral of misfortune.''

Cara previously opened up about her mother's drug addiction affected her childhood.

She said previously: ''I grew up in the upper class, for sure. My family was kind of about that whole parties-and-horse racing thing. I can understand it's fun for some. I never enjoyed it.

''It shapes the childhood of every kid whose parent has an addiction.You grow up too quickly because you're parenting your parents. My mother's an amazingly strong person with a huge heart, and I adore her.

''But it's not something you get better from, I don't think. I know there are people who have stopped and are fine now, but not in my circumstance. She's still struggling.''