British heavyweight champion Danny Williams suffered a shock defeat to Albert Sosnowski on Saturday night at the York Hall in Bethnal Green.
Sosnowski was a late substitute and not expected to trouble Williams unduly, but he was in control throughout the contest and knocked his opponent down in the eighth round, with the fight then stopped.
Williams had been due to defend his title with a rematch against John McDermott, whom he beat in July, but his opponent was forced to withdraw last month due to a rib injury.
There was a controversial moment in the second round when Williams, who is no stranger to penalty points, caught Pole Sosnowski with his head, damaging the 29-year-old's left eye.
Sosnowski, who is based in Brentford, competed well with Williams from the off and it was clear the 'Brixton Bomber' was in for a tough night.
The intensity of the contest increased in round four with Williams landing jabs on a few occasions but Sosnowski's belief did not waver and he punched the air at the end of the three minutes.
Williams, who beat Mike Tyson in 2004, appeared to be struggling to stay with the pace of the 10-round contest and it was Sosnowski making the running.
It got worse for Williams in the eighth round as he was dumped on the canvas by the left hand of Sosnowski, staggering to his feet just in time to beat the referee's count.
But it was only a temporary reprieve for the 35-year-old as the contest was stopped moments later.
Williams refused to do interviews after the fight with speculation he could now choose to retire, although his British title was not on the line on Saturday.
Sosnowski insisted his victory need not be the end of Williams' career, saying: "Danny can come back."
The Pole admitted he was stunned by the victory having stepped in with only a week's notice.
"I was here to win and I did it," he told ITV4. "I'm very tired, very proud, very happy. I did not have any pressure in my mind, I went to the ring and just boxed."