Amir Khan's world title rematch against Lamont Peterson has been cancelled following the American champion's failed drugs test.
It emerged earlier this week that Peterson, who controversially beat Khan in December to capture the Bolton fighter's WBA and IBF light-welterweight titles, had tested positive for a banned steroid.
The news cast doubt over the pair's May 19 rematch in Las Vegas - with Golden Boy Promotions and Khan himself now confirming that the bout has been scrapped.
Khan took to Twitter to announce the clash would not go ahead and laid the blame solely at Peterson's door, before his promoters confirmed the bout was off.
Khan tweeted: "The fight is off! sorry everyone the only person to blame is @kingpete26 I'll be looking for a opponent to fight June 30th."
Golden Boy chief executive Richard Schaefer had revealed that Peterson tested positive for a banned steroid, raising questions over whether the Mandalay Bay showdown would go ahead as the Nevada State Athletic Commission considered whether to grant him a licence.
Khan's team seemed open to the bout going ahead but remained cautious, insisting earlier in the week that the fight was still on for the time being, before the British fighter began making ominous comments on Twitter on Wednesday night.
"We are waiting now on the Vegas Commission, to make a final decision," he tweeted.
"Petersons camp admitted they took he took the testosterone before the first fight.
"I've worked so hard since the age of 8 to achieve my goals and dreams in the sport and Boxing is a dangerous sport a toe to toe battle someone can seriously get hurt especially with an unfair Disadvantage, we need to put a stop to this, I still believe they are my belts, I want to thank everyone for their support.
"Let's hope the right thing will be done!"
He then tweeted that the fight was off, with Golden Boy confirming the news soon after.
A statement from Golden Boy read: "A failed pre-fight drug test administered by the Voluntary Anti-Doping Association (VADA), coupled with the Nevada State Athletic Commission's (NSAC) legal inability to hold a formal hearing on the matter of licensing Lamont Peterson for his Saturday, May 19 rematch against Amir Khan until Tuesday, May 15, has forced the cancellation of the event."
According to Schaefer, Peterson tested positive on both 'A' and 'B' samples from a test submitted in March. However, a subsequent, separate test submitted in April was found to be negative.
The issue was referred to the NSAC, who were due to hold a meeting on Tuesday, May 15, but Golden Boy decided that would be too close to the fight.
NSAC executive director Keith Kizer said: "The commission were due to have a special meeting on May 15. I'm guessing that's not enough time for the promotion.
"We'd be willing still to do that for the good of the sport and the other fighters, the fighters on the undercard.
"It's their call [Peterson's camp] whether they want to request that meeting."
lost his WBA and IBF light-welterweight titles to Peterson on a split decision in Washington in December, a verdict that has been hotly disputed ever since.