Kimmel famously grilled Leno on-air at the height of the 2010 Tonight Show controversy and has since said that he simply doesn't find the comic funny.
The Jimmy Kimmel Live host told Larry King Now that his dislike of Leno actually dates back to the way the presenter's then-agent aggressively fought for him to win The Tonight Show over David Letterman in 1992.
"For me, it started with Letterman, and it started with a guy [Leno] who, at least from my standpoint, became famous on the Letterman Show," Kimmel explained.
He went on to say: "I always felt weird about how Jay got that 11.30 spot. Of course, that was NBC's decision, but the whole thing seemed pre-meditated to me."
Jimmy Kimmel Live will begin competing directly against Leno's Tonight Show and The Late Show with David Letterman in January.
Kimmel has said that he will not change his ABC late-night show's format in a bid to win Leno or Letterman's viewers.
Watch Jimmy Kimmel roast Jay Leno on-air below: