Selena Gomez’s mom says Taylor Swift is the person her daughter can ‘tell anything’ (exclusive)

Selena Gomez and Taylor Swift's close bond is one that has withstood the test of time.

ET's Katie Krause sat down with Gomez's mother, Mandy Teefey, for a Facebook Live chat on Thursday, in which she talked about the two superstars' long-lasting friendship. This past Saturday, Gomez made a surprise appearance during Swift's show at the Rose Bowl in Pasadena, California, where she called Swift her "best friend."

"What I love about that friendship is it's so solid, and with Taylor, I feel like they can tell each other anything, and it will be an honest, in-your-best-interest kind of relationship," Teefey says. "It's not about anything else, and it's one you don't just find out here."

Teefey also praised 28-year-old Swift's authenticity.

"With Taylor, what you see is what you get," she notes. "She is who she is, and that's why she's so grounded and, like, works so hard, and she's always been there for Selena. It's so hard to find someone who is kind of the same audience and it's so cutthroat right now .... they came up together, they just have never parted, so it's really a true friendship."

Teefey shared that Swift's friendship extends to her youngest daughter, 4-year-old Gracie, who also spent time with the GRAMMY-winning singer backstage at her recent shows.

"It's really cute because when Gracie was born, Taylor bought her, like, boxes of clothes," she shares. "So, when Gracie went backstage to talk to her, Gracie had bought her a bunch of clothes too, and wanted to give it back."

"I was, like, 'Yeah, she probably doesn't need these but OK,'" Teefey continues with a laugh. "And in line, she kept saying, 'What was I supposed to say again?' And I was just like, 'Thank you for the clothes,' even though she's, like, seen her [since]."

On Saturday, 25-year-old Gomez gushed about her friendship with Swift onstage before the two sang her hit, "Hands to Myself."

"The reason why she’s been one of my best friends is this person has never, ever judged a single decision I’ve made," Gomez said as the audience cheered. "She’s always met me where I’ve been. She’s encouraged me when I’ve had nothing to be encouraged about. And I don’t know if I would be as strong as I am if I didn’t have you and your family in my life.”