Crafting the perfect marriage proposal can take careful planning. Proposing in front of Taylor Swift? That's on another level.

When a young man knelt down and surprised his girlfriend at Friday's "Reputation" concert at Lincoln Financial Field in Philadelphia, Taylor Swift looked shocked.

"They walk into the meet and greet and he says 'We met 5 years ago at the Red Tour' and then … #thirdwheel," the singer, 28, captioned a sequence of Instagram photos that documented the moment in the backstage Rep Room.

It turns out this kind of romantic gesture is not whipped up on the fly. According to his Twitter account, Anthony, the groom-to-be, started planning over a month ago.

"Our love story started at a RED TOUR show in Philadelphia back in 2013," Anthony explained in a tweet July 10. "Our love story continues this Friday at the REP TOUR. Nothing would make this proposal more special than having her there!"

Anthony said he and his girlfriend, Stephanie, have listened to Swift's music together throughout their relationship. "I can't thank Taylor enough for bringing us closer," he wrote.

The key to Anthony's plan was mobilizing an army of other diehard "swifties" to retweet, tag Swift's official social-media accounts, and help him decide how, when and where to pop the question.

And the rest is history.

No word yet on whether Swift will officiate at the wedding.