Barenaked Ladies -- My Ex-Bandmate Is Screwing Me Out of 'Big Bang Theory' Money

Fun fact -- The Barenaked Ladies wrote the theme song for "The Big Bang Theory".

Not so fun fact -- a former member of TBL says he hasn't received a dime for the work ... even though its TV's #1 comedy.

According to legal docs, former front man Steven Page claims he was promised 20% of all proceeds from the song. He says band member Ed Robertson is the only one collecting and has kept all the money for himself.

Page says he isn't sure of the total profits generated from the theme song but believes they are in excess of $1,000,000 -- and he's suing for his 20%.

Unravel the mystery ...