What happens when Beyoncé and Taylor Swift are side by side at a Justin Timberlake concert? They sing along, dance, and jump up and down like true superfans. It all happened during Justin's 20/20 Experience show at Barclays Center in Brooklyn, NY, on Sunday. Fortunately, an audience member captured the priceless moment in video and shared it on Instagram. Although you can't see much of Beyoncé's face, it's clear Taylor is putting her animated expressions to good use. All things considered, the sighting suggests Taylor's "#bestbirthdayEVER" got even better after her party with Bey, Jay Z, Justin, and even more stars on Friday. Check out the clip above, and then catch up on the latest viral videos.