Foiled again!

Once again, Amir Khan, a top welterweight contender and former unified junior welterweight titleholder, was passed over by Floyd Mayweather, who announced Tuesday that he would fight Andre Berto on Sept. 12 in what he claims will be his final fight.

Khan has been dying to fight Mayweather, who has dangled the fight at Khan multiple times over the past couple of years. Khan was the top candidate to get the fight. Mayweather himself said that on more than one occasion.

In 2014, for example, Mayweather conducted an online fan poll to pick his next opponent. Khan topped the voting, garnering 57 percent of the more than 35,000 votes. So what did Mayweather do? He picked Marcos Maidana instead. And then he picked Maidana again for a rematch instead of Khan. And then, understandably, he finalized the fight this past May against Manny Pacquiao. All the while, Khan was sitting there as the backup plan in case the Pacquiao fight went unmade yet again.

"I'm disappointed not to have got the fight for what is the third time after having been one of the frontrunners. However, there are many big fights out there for me and I'm going to continue working hard to establish myself at the top of the welterweight division."

And now that Mayweather is ready to fight again after beating Pacquiao, Khan was once again a leading candidate -- and a more deserving candidate than he had been previously. He is also a much more deserving candidate than Berto, who is 3-3 in his last six, has not won a notable fight in years, was suspended at one point for a failed steroid test and suffered losses to two guys Mayweather beat easily (Robert Guerrero and Victor Ortiz).

In fact, it is easily arguable that Berto’s biggest win came by disputed decision against Luis Collazo in a life-and-death fight. The same Collazo that Khan routed.

Unlike Berto, Khan has won five fights in a row, including three in a row against good opposition, including former titlist Collazo on the Mayweather-Maidana I undercard in a fight ostensibly to set him up for a shot at Mayweather. Then Khan looked even better in December as he routed former titlist Devon Alexander in a near shutout. In May, Khan outpointed former junior welterweight titlist Chris Algieri in a fight that was again supposed to be a tuneup for a possible Mayweather shot.

But once again, Mayweather overlooked Khan, whose speed, size and athleticism many think would give Mayweather some problems.

Mayweather’s decision to bypass Khan again would be understandable had he done so in order to fight welterweight titlist Keith Thurman or perhaps former titlist Shawn Porter, or even to unify belts against Kell Brook, the fine fighter from England who beat Porter for the belt but it largely unknown in America.

And had Mayweather declined to fight Khan in order to dare to be great by fighting a top middleweight -- Gennady Golovkin, even at a catchweight, anyone? -- that would be applauded.

But Mayweather, who claims to be TBE (the best ever) instead opted for the path of least resistance against Berto -- and will have the audacity to ask the public, still smarting from the Pacquiao money grab, to pay $64.95 ($74.95 in HD!) on Showtime PPV after dangling the prospect of a free fight (on CBS).

Amir Khan has been the front-runner to face Floyd Mayweather for the last couple of years, but he never got the chance. Ed Mulholland/Golden Boy/Getty Images

Khan needled Mayweather with his big mouth and essentially begged for the fight, which did not go over well with Mayweather. But now that he has been officially left as a bridesmaid once again, Khan, to his credit, took the high road even though it has to be very hard for him to watch the lesser Berto, with whom he shares trainer Virgil Hunter and with whom he has trained side by side, get the fight of a lifetime.

“I’m disappointed not to have got the fight for what is the third time after having been one of the front-runners,” Khan said. “However, there are many big fights out there for me and I’m going to continue working hard to establish myself at the top of the welterweight division. Floyd Mayweather has fought the biggest names throughout his career and has earned the right to face whoever he chooses.

“I wish my stablemate Andre Berto and trainer Virgil Hunter the very best of luck in the fight. I have seen how hard Andre trains and works and know that he is ready to give Floyd a very tough night.”

Nobody really expects that Berto will give Mayweather a tough fight but what will undoubtedly be tough is for Khan to watch it.