Great Britain's men finished just outside the medals as they came fourth in the 4x100 metres medley relay at the Aquatics Centre.
Liam Tancock, Michael Jamieson, Michael Rock and Adam Brown put up a brave fight but they were edged out of the medals in three minutes 32.32 seconds.
All eyes were on Michael Phelps as he brought to an end a career few can ever hope to match as he claimed his 18th Olympic gold medal as the United States won the race in the final swimming event of London 2012.
The 27-year-old now has 22 medals - 18 gold, two silver and two bronze - over four Olympics, his Games career starting in Sydney 12 years ago when he was fifth in the 200m butterfly.
Six golds and two bronze medals in Athens was followed by his historic eight gold medals in Beijing four years later.
He swam the butterfly leg and handed over to Nathan Adrian in first place for the freestyle as the United States clinched another title in 3mins 29.35secs.