Great Britain's men's sprint relay team have missed out on a place in the final of the 4x100 metres following a mistake in the baton changeover at the Olympic Stadium.
The host nation were disqualified when anchor leg runner Adam Gemili set off too early as he was about to take the baton from Danny Talbot.
The 18-year-old athlete slowed down dramatically, but the changeover still occurred outside the designated area.
Gemili sprinted for the line and came home second, but realised their mistake, putting his hands on his head in despair.
Jamaica, without Usain Bolt, qualified safely, but the United States were the quickest through in a new national record of 37.38 seconds.
Gemili told the BBC: "I went off and maybe I went a bit harder...I don't know. We really could have been in contention in the final had we made it. It really is disappointing. I think I went on the check mark maybe a tiny bit early."
For Dwain Chambers, who ran the second leg, this was almost certainly his last race at an Olympics and he was keen to keep his teenage team-mate's spirits up.
He said: "We're proud to have been here representing our country. Adam's had a fantastic start to his season.
"This is his first or second season in athletics and he was asked to do a big task. I'm proud of him more than anything else.
"We have to build as a team and hopefully can do better throughout the summer and next year."