But their WEC 53 main event matchup will be more than just an answer to a trivia question; it will also determine the No. 1 contender to the UFC lightweight championship.
That's the word according to UFC president Dana White, who told reporters of the plan during a conference call to formally announce the UFC-WEC merger.
We won't know exactly who makes it into the title match until January. On Jan. 1, current UFC champion Frankie Edgar will defend his belt for the second time, this time against Gray Maynard.
The winner of that bout will then faceoff with the reigning WEC champion to unify the belts.
The other part of the equation will be decided on Dec. 16 at WEC 53 when Henderson and Pettis tangle.
Henderson (12-1) captured the interim title in October 2009 and then made it official with a submission over Jamie Varner in January 2010. In his first full title defense, he also submitted Donald Cerrone with a guillotine.
Henderson has never lost under the Zuffa banner and has won 11 straight fights overall.
Pettis (11-1) earned his title shot with three straight stoppage wins, defeating Danny Castillo by KO before beating Alex Karalexis and Shane Roller via tapout.