Michael Phelps was not included on the American team for the worlds in Kazan after his arrest for driving under the influence of alcohol last September and many speculated his comeback had hit the buffers.
The 30-year-old Phelps has certainly proved his doubters wrong with a trio stunning performances at the U.S. national championships in San Antonio, Texas.
The 22-time Olympic medalist won the 100m butterfly in 50.45 seconds, almost a second faster than the time he set to win gold in the event at the 2012 Games in London.
It also sent an ominous warning to his arch-rival, South African Chad le Clos, who won the world title in the 100m butterfly, but in a slower time of 50.56 seconds.
The flamboyant le Clos had put some added spice into the rivalry by pointing to the fact his winning performance in Kazan had been done in a time not bettered by Phelps in four years.
Eight hours later, Phelps had made his point by bettering the mark set by le Clos.
Phelps holds the world record for the event of 49.82 seconds, set at the Rome world championships of 2009, when competitors were allowed to wear faster all-body swimsuits, which were eventually banned by the sport's governing body FINA.
Le Clos was completing the butterfly double in Kazan, having won the 200m earlier in the week, showing the sort of form that had seen him pip Phelps to the gold in that event in London.
But again he was upstaged by Phelps, who posted a time of one minute 52.94 seconds on his way to his own double in San Antonio, the best in the world this year, and again faster than le Clos' effort in Kazan.
Phelps called it "close to probably my best 200 fly ever" and shows that with the Rio Games just a year away he is set to add to his all-time Olympic record medal haul.
Phelps' absence from the U.S. team in Kazan was keenly felt in events such as the 4x200m freestyle relay, where its previously invincible team was surprisingly beaten to silver by Britain, anchored by individual 200m freestyle champion James Guy.
But while the U.S. men generally underperformed without its talisman, the undisputed star of the championships was 18-year-old Katie Ledecky from Washington D.C.
She completed a clean sweep of the freestyle events Saturday, winning the 800m in a world record time, to add to her earlier successes in the 200-400 and 1500m events. Ledecky also won gold in the women's 4x200m relay to take her tally to five.
Only Phelps, with five at the 2007 world championships, has won more individual gold medals at the biannual event and both are primed to be the backbone of the United States team in Rio next year.
Phelps rounded off his triumphant weekend at the U.S. Nationals by winning the 200m individual medley Sunday night in one minute 54.75 seconds, his third 2015 world leading time.
"I'm very happy where I am right now. This is a great foundation, a place where we've never really been in a long time leading up to an Olympics," Phelps told the official USA Swimming website.
With Phelps absent and despite Ledecky's heroics, it was China which topped the medal table at the end of the week-long world championships, the first time since 2001 that the U.S. has not been in that position.
But there was controversy on the final day as China's Sun Yang did not take his place for the final of the men's 1500m freestyle.
Sun has dominated the distance freestyle events at the Olympics and world championships in recent years and his absence was described as "shocking" by the official Twitter feed of FINA.
The 23-year-old Sun later told reporters that he had pulled out of the medal race because of heart problems, which he claimed had also troubled him after winning the 800m final.
"After the 800m competitions, I didn't feel well in my heart. I felt uncomfortable in the warmup tonight so I had to give up the idea of competing," he said.
Sun served a three-month ban for taking a banned stimulant, Trimetazidine, in 2014.
Trimetazidine is a prescription drug used to treat heart palpitations.
Italy's Gregorio Paltrinieri took the gold, having been fastest in morning qualifying, with Sun third best.