Personally, I'd like to think these two have been A1 since the day one, and here's a little anecdote to support it, courtesy of Grohl himself.While seated in front of an audience on June 22 in Cannes, the singer and songwriter told a story about the time Swift saved his ass in front of Sir Paul McCartney.Here's how is went down:Grohl, Swift, and McCartney were all at a small party together a while back, when McCartney invited Grohl to play a song on his piano. Grohl froze because he cannot play the piano. Not only that, but all of McCartney's guitars were left-handed, and Grohl is a righty.Also, he had smoked some pot beforehand and was "super high."Then, "like fucking Batman," Swift popped up out of the audience and said, "I'll play a song!" So, then she gets on the piano and starts playing a song and Grohl realizes he recognizes the tune. Much to his stoned surprise, she starts playing a piano version of his band's song, " Best Of You ."Hear Grohl tell the full story below, and then sing an acoustic version of the song.