Taylor Swift says that her mother Andrea's cancer has returned, and it could be serious.

The pop star spoke up in a piece she wrote for Elle Magazine that published online on Wednesday (March 6). No. 24 on her 30 Things I Learned Before 30 list reveals that both parents have had cancer, and Andrea Swift's is back.

"It’s taught me that there are real problems and then there’s everything else," the "Dear John" hitmaker writes. "My mom's cancer is a real problem. I used to be so anxious about daily ups and downs. I give all of my worry, stress, and prayers to real problems now."

Swift has stayed mostly quiet about her mother's health since first revealing the diagnosis in April 2015 and never definitively let fans know her mother was cancer-free. At that time Andrea encouraged her daughter to share the news.

"She wanted you to know because your parents may be too busy juggling everything they've got going on to go to the doctor, and maybe you reminding them to go get checked for cancer could possibly lead to an early diagnosis and an easier battle," Swift said at the time, "Or peace of mind in knowing that they're healthy and there’s nothing to worry about."

A few weeks later, Andrea Swift introduced her daughter during the 2015 ACM Awards in Texas. It was the 50th anniversary of the ACMs and Mrs. Swift shared stories while looking strong and healthy. She's a familiar face to the singer's longtime fans, often organizing backstage experiences with her daughter.

Elsewhere in the 30 Things piece Swift talks about relatively superficial items like skin and hair care, in addition to issues like sexual assault, social media trolls and relationship failures.

Country Stars Who've Been Touched by Cancer: