No one lauds the “Wicked” quite like Billie Eilish — at least when she is in full Ariana Grande-fangirl mode, as she was in interviewing her longtime singing heroine after a screening of the movie musical in Hollywood on Tuesday night. The Q&a, held for SAG members at the Directors Guild of America’s theater, had Eilish doing the moderating at the personal behest of the film’s Oscar-nominated Glinda.

“My team was like, ‘Who would be a cool person to do this? Who’s your dream person?'” Grande said at the outset. “I was like, ‘Billie, [but] she’s not gonna say yes.’ She’s too busy. She’s too fabulous. It’s too much. But she said ‘Yes,’ and I was like, ‘Oh, shit. Now I’m so nervous.'”

Eilish piped up with her youthful-worship credentials. “I love this girl so much and I love this...