Selena Gomez Surprise Guest at Taylor Swift Rose Bowl Reputation Concert

Taylor Swift brought her long-time bud Selena Gomez up on stage Saturday night at her Rose Bowl concert.

Selena and Taylor sang "Hands to Myself" -- Selena's song -- in the middle of the "Reputation" concert in Pasadena.

The stadium packed for a second time. Taylor also performed there Friday night.

Selena told the crowd, about Taylor ... "The reason why she has been one of my best friends is because this person has never, ever judge a single decision I've made."