Rossi celebrated victory before learning of his penalty
Max Biaggi was handed victory at the British Grand Prix when Valentino Rossi was dramatically given a penalty over three hours after the race ended.
World champion Rossi celebrated what he thought was a victory on the podium before race officials realised he had overtaken Carlos Checa under a yellow flag at the start of lap two.
The yellow flag was raised following a crash involving Tohru Ukawa.
An investigation was held and Rossi later penalised 10 seconds, moving Sete Gibernau into second place ahead of the Italian.
The two Ducatis of Loris Capirossi and Troy Bayliss were fourth and fifth respectively.
"The final result is disappointing," Rossi said. "I did nothing wrong intentionally. I never saw the flags. I am disappointed but rules are rules and I can't argue with the law.
"
I only hope the outcome of the race does not affect the championship
"
Valentino Rossi
"I didn't take advantage of the situation and went on to win the race."
In the race, Rossi had recovered from a poor start that saw him slip three places to seventh.
He stormed through the field and took the lead when arch-rival Biaggi made a mistake through the chicane on lap 13.
From there, Rossi held on for what appeared to be his fourth victory at Donington, before race officials ruined the world champion's day.
Rossi's lead over Gibernau in the championship at the halfway point of the season was consequently cut to 34 points, while Biaggi moved to within three points of the Spaniard in third place in the standings.
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"I only hope the outcome of the race does not affect the championship," the 24-year-old Rossi added.
"As a rider I sympathise with Rossi," said Biaggi.
"I understand what he must be feeling because the same happened to me in a race in Barcelona in 1998 which I won on the track.
"The only difference is that that decision subsequently cost me the championship."
MotoGP results:
1. Max Biaggi (Italy) Honda - 46 minutes and 06.688
2. Sete Gibernau (Spain) Honda - 46:13.826
3. Valentino Rossi (Italy) Honda - 46:15.482*
4. Loris Capirossi (Italy) Ducati - 46:19.729
5. Troy Bayliss (Australia) Ducati - 46:22.967
6. Carlos Checa (Spain) Yamaha - 46:33.773
7. Noriyuki Haga (Japan) Aprilia - 46:34.350
8. Nicky Hayden (U.S.) Honda - 46:38.700
9. Shinya Nakano (Japan) Yamaha - 46:41.487
10. Colin Edwards (U.S.) Aprilia - 46:41.689
*Rossi handed 10-second penalty
World championship standings:
1. Rossi - 167 points
2. Gibernau - 133
3. Biaggi - 130
4. Capirossi - 84
5. Bayliss - 64