Selena Gomez and Taylor Swift's friendship is ''so solid''.

The 'Heart Wants What It Wants' hitmaker's mother Mandy Teefey says her daughter's friendship with the 'Shake It Off' singer is one of those ''in-your-best-interest kind of relationship''.

Speaking to Entertainment Tonight, Mandy said: ''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. It's not about anything else, and it's one you don't just find out here. With Taylor, what you see is what you get. 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.''

Selena recently joined Taylor on stage during her 'reputation' world tour, where she gushed about how Taylor ''changed'' her life.

She told the crowd at the Rose Bowl in Pasadena: ''I want to say thank you to my best friend of about 12 years, almost 13. And the reason why she has been one of my best friends is because this person has never, ever judged a single decision I've made.

''She's always met me where I've been. She encouraged me when I've had nothing to be encouraged about. I don't know if I would be as strong as I am if I didn't have you and your family because you changed my life.''