"Wait, who is Justin Bieber?" ... said nobody, ever.
The Bieb Train was all up in the Twitterverse this week, posting six of the most popular photos people shared. British boy band One Direction held their own, though, with three of the top 10 pics -- including the most shared. It's the USA vs. the UK: teen-heartthrob-Instagram-sharing edition.
Our friends over at Skylines went through 52,846,148 photos from the week to compile this list. Browse through the gallery above to see the top 10.