Sherdog.com breaks the news that Chael Sonnen - known as the guy who came closest to dethroning Anderson Silva - had the help of performance-enhancing drugs that night:

According to California State Athletic Commission Executive Officer George Dodd, Chael Sonnen has been notified that he failed post-fight drug screening following his loss to Anderson Silva at UFC 117, which was held Aug. 7 at the Oracle Arena in Oakland, Calif.

... In a conversation the day before, Dodd declined to comment on the situation, other than answering that all fighters from UFC 117 had passed drugs-of-abuse scans, but that the commission was still waiting on performance-enhancing drug screens from the event.

Dodd did not state which banned substance was red-flagged, but with a clean drugs-of-abuse scan it is clear the positive test was for a performance-enhancing substance.

Silva's manager Ed Soares hits the nail on the head with his comment:

"If it’s true, I feel really bad for him," said Soares. "I know he did it to himself but it is really sad, he put on such a great performance that night. It is just a shame it will be tarnished."

Sonnen's pre-fight trash talk, coupled with his 24 minutes of dominating the champ, has brought him a ton of new fans and even netted him a high-profile rematch for early 2011. Even though he lost that bout, it was by far the best performance of his career, but that failed drug test tarnishes everything. He will likely get fined and suspended for this, making it likely that the fight gets postponed, or even canceled. Either way, even if the UFC decides to go on with the bout, the rematch certainly loses a lot of its luster.