Ryan Seacrest and Justin Bieber Celebrate American Top 40's 40th Anniversary. Seacrest is the program's second host. AT 40 was originally hosted by Casey Kasem.
American Top 40's 40th Anniversary
Ryan Seacrest and Justin Bieber Celebrate American Top 40's 40th Anniversary
American Top 40 is one of Radio's longest running syndicated programs.
Ryan Seacrest and Justin Bieber Celebrate American Top 40's 40th Anniversary
Photo: Sadao Turner/Ryan Seacrest Productions
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