BERLIN: "What can I say?" asked Usain Bolt, having just demolished his 200m world record in 19.19sec at the World Athletics Championships last night. What could anyone say? The Jamaican, who turns 23 years old today, becomes the first man to hold the 100m and 200m world and Olympic titles at the same time, following his triumphs in last year's Olympics.

"I keep telling you guys, my main aim is to become a legend, that's what I'm working on," he shrugged. "It's a great feat for me to have broken my world record. I didn't know I was going to break it."

Bolt did not just break the record, he destroyed it, taking 0.11sec off the 19.30 mark he had set in Beijing last year, with Panama's Alonso Edward claiming silver in 19.81 and the American Wallace Spearmon the bronze in 19.85.

He achieved the feat without a full season of training behind him – having missed four weeks after a car accident earlier this year. Could he run a sub-19 race? "I guess so, I don't know," he said.

While the world struggled to understand what they had witnessed, Bolt had a simple explanation. "I said early in the season that I had to get my start right," he said. "I worked on it. That was the key in this final: I got my start right." His reaction time of 0.133sec was the best in the field.

Inevitably though, the question of performance-enhancing drugs was raised. Bolt was direct in his answer. "I keep telling everybody I'm clean; if they don't believe me there's nothing I can do. I don't know what else I can say to convince people I'm clean, only to just run and stay clean."

Bolt said he was not upset by the speculation. " I don't get offended because I know year after year people have run fast and then they have tested positive. I just continue running fast and one day people will stop asking that question."

Spearmon, who took bronze, said: "When we first started running in 2005Michael Johnson had the record of 19.32 and everyone kept saying it couldn't be broken. Now Usain's done it and now the world believes. Somebody's going to break it again – maybe even him– it's just a matter of time."

Asked if it was harder than his equally amazing double in Beijing, Bolt said: "Not mentally, physically it was harder because I wasn't in the best of shape. The rounds took a lot out of me this time. I just want to go home and sleep. It definitely means a lot because I showed people that last year wasn't a joke. I went through some problems this season but I came out here and I showed the world with hard work and dedication what is possible."

He added: "I definitely came here trying to double. Now I'm double world champion, I'm double Olympic champion so I have to defend my titles. If Queen Elizabeth knighted me would I get the title 'Sir Usain Bolt?' That sounds very nice."