Joe Joyce was left stunned after falling short in his bid to be crowned Olympic super-heavyweight champion against Frenchman Tony Yoka in the last action of the Rio Olympics for Great Britain.
Joyce greeted the final bell convinced he got the better of Yoka and had emulated Anthony Joshua, who was watching at ringside, in claiming gold in the men's +91kg division.
But two of the three ringside judges favoured Yoka's apparent accuracy in a split decision verdict which was greeted with loud booing by sections of the predominantly Brazilian crowd.
Conlan was critical too, commenting on Twitter: “AIBA don't cheat... Said no one ever!!!! Hard luck big @JoeJoyce_1 your not the first and you'll not be the last! #MiddleFingerUpToAIBA”.
If the 30-year-old's defeat did not rank among the most controversial of a difficult Games for the sport, it did beg more questions over the new scoring system as Joyce's greater aggression was overlooked.
As Yoka launched into an extended bout of celebrations, Joyce asked: "Why's he going on like he won it? It frustrates me that he can be so cocky and confident when I feel I battered him."
Joyce's style had been derided by Yoka in the build-up to the final, with the Frenchman describing him as a "robot" and questioning his punching power.
The pair had unfinished business after a controversial World Championship semi-final in Doha last year, when Yoka was controversially given the verdict and went on to win the title.
Joyce was the aggressor in the opener, landing first with a nice right hand, and pushing forward looking to squeeze shots through his opponent's tight guard.
The heavier shots continued to come in from the Briton, but Yoka enjoyed persistent success behind his left jab, which was enough to shade it on two of the three judges' cards.
Joyce continued his relentless push forward in the second, with Yoka a little looser and relying more on snaking counter-shots, again catching the judges' eyes.
It effectively meant Joyce needed a knockout to win the last, and despite his best efforts Yoka survived to take the victory on two of the three judges' cards.
It meant another gold medal for France after Yoka's girlfriend, Estelle Mossely, won the women's lightweight title on Friday.
Joyce added: "I thought I was working him to the body and head and I thought I was penetrating his guard.
"I thought I won the rounds. I did enough to win the gold medal. I thought I took it to him and I thought I'd be coming back to talk to you guys over the moon.
"I lost to him at the worlds and I thought it was close. I wasn't as fit that time and I thought this time I was more than 100 per cent and I still didn't come away with the gold medal."
Joyce's silver medal means Great Britain come away from the Olympic boxing competition having won a medal of every colour.
Nicola Adams retained her women's flyweight title on Friday and Josh Buatsi earned an impressive bronze in the light-heavyweight division earlier in the week.
But the tournament was overshadowed by a series of controversial decisions, chiefly those involving defeats for Kazakstan's Vassiliy Levit and Ireland's Conlan.
Midway through the tournament, six judges were sent home and AIBA's executive director Karim Bouzidi was "re-assigned" to a new position within the company.