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"And then I look around ... and all of the guitars are left-handed (because Paul McCartney's left-handed)."
The rocker admitted that he thought he was "screwed" ... and then Taylor Swift came to his rescue.
"All of a sudden, Taylor Swift stands up and says, 'I'll play a song'."
Swift sat at the piano and started playing while Grohl, feeling like he had to contribute, grabbed one of McCartney's left-handed guitars and struggled to jam along to the mystery tune.
"I look at my wife and I'm like, I know this f***ing song. And she (Swift) was f***ing playing our song, Best of You. As if I weren't high enough, that f***ing blew me into outer space ... I just lost my mind."
During the story, Grohl described Swift as "Batman" as she was there to save the day exactly when he needed help.
"It's like, 'Oh, thank god. Taylor Swift's here. Like f**king Batman when you need him.'" Grohl said.
Warning: Video contains explicit language