Let's see who the true best friend is!
Jessica Biel and Justin Timberlake appeared on The Tonight Show with Jimmy Fallon.
Timberlake recently had to postpone his tour due to his vocal chords being damaged.
Hindsight: & All The Things I Can't See In Front Of Me is Timberlake's new book that he recently released.
After promoting his new book, they all played a little game called The Best Friends Challenge.
It tested Jessica and Jimmy's knowledge of JT.
Who is the real BFF?!
Watch to find out!