Usain Bolt will have to hand back one of his nine Olympic gold medals after Jamaican team-mate Nesta Carter tested positive for a banned substance.Carter was part of the Jamaican quartet that won the 4x100m in Beijing in 2008.His was one of 454 selected doping samples retested by the International Olympic Committee (IOC) last year, and has been found to contain the banned stimulant methylhexaneamine.Bolt, 30, completed an unprecedented 'triple triple' in Rio last summer.He won gold in the 100m, 200m and 4x100m relay to add to his successes in the same events in 2008 and 2012.Carter, 31, was also part of the squad that won the event in London five years ago and helped Jamaica win at the World Championships in 2011, 2013 and 2015.He ran the first leg for Jamaica's 4x100m relay team in Beijing, which also included Michael Frater, Asafa Powell and Bolt.The team won in a then world record of 37.10 seconds, ahead of Trinidad and Tobago and Japan, who will now have their medals upgraded. Brazil will receive bronze.Russia's Tatiana Lebedeva has also been stripped of her Beijing long jump silver after dehydrochlormethyltestosterone was found in one of her samples.The test and what happened next?Carter was tested on the evening of the Beijing final in 2008 but that was found at the time to contain no "adverse analytical finding".More than 4,500 tests were carried out at those Games, but just nine athletes were caught cheating.An anomaly was discovered in Carter's submission following the IOC's decision to retest 454 samples from Beijing using the latest scientific analysis methods.Carter and the Jamaican National Olympic Committee were told of the adverse finding in May - before the Rio Games - and told his B sample would be tested.It was reported by Reuters in June that Carter's A sample had been found to contain methylhexanamine, which has been on the World Anti-Doping Agency (Wada) prohibited list since 2004.It was reclassified in 2011 as a "specified substance", meaning one that is more susceptible to a "credible, non-doping explanation".Sold as a nasal decongestant in the United States until 1983, methylhexanamine has been used more recently as an ingredient in dietary supplements.Britain's two-time Olympic silver medallist Roger Black on BBC Radio 5 liveIt takes the shine off Bolt's achievement. Eight doesn't have the same ring - 'double treble, plus two'.It will be really frustrating for him. You can only account for yourself, you cannot account for your team-mates.We know it has nothing to do with Usain Bolt - it will not damage his reputation - but it will affect it, take shine off it and he won't be a happy man.When I hear stories like this, a part of me does celebrate. If athletes think they have got away with, then with retrospective testing they can never sleep peacefully.It has to be the strongest deterrent the sport now has. Even when athletes retire they can still have their medals taken away. That is a really good deterrent.