Ariana Grande Calls 'Wicked' Popularity 'Surreal,' Praises Cynthia Erivo

Ariana Grande can't believe "Wicked" defied the odds by becoming the highest-grossing Broadway musical movie adaptation ever ... calling the flick's growing popularity "surreal."

We caught up with the pop star outside CBS Studios in NYC on Tuesday, where she met with her adoring fans and signed a number of autographs -- feeling as "Popular" as ever.

However, Ari made it clear she's blown away by audiences' response to the movie ... noting she and her "Wicked" peers are all moved by the worldwide attention.

Yet, it's her friendship with co-lead Cynthia Erivo that Ariana is cherishing the most after wrapping the musical movie.

When asked whether she planned to be friends with Cynthia for life, Ariana declared "Of course!" and quipped the Broadway veteran was "stuck" with her moving forward.

Cynthia was equally giddy with all the "Wicked" affection ... we caught up with the British actress on Monday, where she happily revealed fans have been bursting into song when running into her.

She also teased an upcoming appearance at the planned "Wicked" sing-along screenings ... though, didn't share the where and the when.

Nonetheless, it's obvious both Ariana and Cynthia have been changed "For Good" from their work in "Wicked"!!!