In 1998, a young Jerome Le Banner took on Brazilian, Espidito "The Black Panther" Da Silva in a W.K.N. World Heavyweight Muay Thai Championship Fight. The fight took place on the undercard of "Evander Holyfield vs. Vaughn Bean" in Atlanta, Georgia and was promoted by the boxing icon Don King.
There may not be another time in history where a high-profile kickboxing/muay thai match takes place on the same card as a boxing world heavyweight championship fight. It's a little surreal seeing King and Le Banner together at the end of the video, and it's definitely worth a watch just to witness a pretty momentous occassion in kickboxing history. The knockout is pretty awesome too (But don't take my word for it).