Youngest Jonas Brother -- the 'bonus Jonas' -- goes to prom in Southlake

There are three Jonas Brothers, Joe, Kevin and Nick -- right? Wrong. There are four Jonas brothers. The youngest JoBro was never in the now-defunct boy band, as he was just 5 years old when his older siblings recorded their first tune.

Well, little Franklin "Frankie" Jonas grew up. And he recently attended prom at Southlake's Carroll Senior High School, Instagram shows:

People.com reports his blonde prom date is his girlfriend Austin.

Asking a date to prom isn't as easy as it used to be. "Promposals" are today's version of a smaller-scale wedding proposal, and many high school students go to great lengths to surprise and shock the person they hope will join them at the big dance. In Frankie's case, he made a Captain America inspired sign that said "I'd be red scared if you didn't make me the Bucky-est man on earth by going to prom with me."

Cute.