Mar 27, 2015  · Years after Justin Guarini competed on American Idol and starred in From Justin to Kelly, the 36-year-old actor is back in some hilarious new ads for Diet Dr. Pepper. The singer and Broadway actor. Dr. Pepper Commercial. Not sure if it’s been covered here, but does anyone else think the Diet Dr. Pepper commerical is making fun of Prince?. Someone mentioned to me that the one imitating…