Taylor Swift revealed her mother, Andrea Swift, has been diagnosed with a brain tumor.

The "You Need to Calm Down" hitmaker made the devasting revelation in her Variety cover story, in which she also discusses her role in Cats and her Netflix documentary, Taylor Swift: Miss Americana. Swift said that a brain tumor was discovered during her mom's course of treatment amid her ongoing battle with cancer.

"She was going through chemo, and that’s a hard enough thing for a person to go through," the singer shared. "While she was going through treatment, they found a brain tumor 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," Swift added.

The 30-year-old pop star also confirmed that her mom's diagnosis is the reason she decided not to go on another world tour to support her new album, Lover. Instead, she'll embark on a shorter concert tour in 2020, dubbed the Lover Festival, so she can be there to support Andrea during her upcoming treatments.

"Yeah, that’s it. That’s the reason," Swift said. "I mean, we don’t know what is going to happen. 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."

"Everyone loves their mom; everyone’s got an important mom," she continued. "But for me, she’s really the guiding force. Almost every decision I make, I talk to her about it first. So obviously it was a really big deal to ever speak about her illness."

Swift addressed her mom's health in her song "Soon You’ll Get Better," in which she sings the heartwrenching lyrics, "I hate to make this all about me/ But who am I supposed to talk to?/ What am I supposed to do/ If there's no you?"