Taylor Swift has revealed new details about her mom’s illness in a cover story with Variety Tuesday.

The singer says that while her mom, Andrea Swift, was receiving chemotherapy for an undisclosed type of cancer, doctors made another heartbreaking discovery.

"While she was going through treatment, they found a brain tumor," she told Variety. "And the symptoms of what a person goes through when they have a brain tumor is nothing like what we’ve ever been through with her cancer before."

"So it’s just been a really hard time for us as a family," she added.

Swift's mom’s health was one of the main reasons she decided not to embark on a full-blown tour this year. Instead, she’s making just four stops in the U.S. -- billed as Lover Fest East and Lover Fest West -- and performing at some festivals in Europe over the summer.

"I mean, we don't know what is going to happen," the singer explained. "We don't know what treatment we're going to choose. It just was the decision to make at the time, for right now, for what's going on."

Swift first revealed that her mom was battling cancer in 2015. She successfully completed treatment, but in March of 2019, Taylor shared that the cancer had returned. The song "Soon You’ll Get Better," on Swift's latest album "Lover" is about her mother’s illness.