There have always been signs that Oleksandr Gvozdyk might make a shock decision, in stark contrast to Oleksandr Usyk, according to the promoter who knows both Ukrainians best.
Ukraine's stunning Olympic 2012 team included Vasiliy Lomachenko, Usyk and Gvozdyk - all three became professional world champions but the latter has called time on his career surprisingly early.
Does that raise new questions about Usyk and Lomachenko, who are the same age and similarly long in the tooth?
Usyk and Lomachenko emerged from London 2012 with Olympic gold medals, the standout performers of a Ukrainian team coached by 'Papachenko', the inspirational father of Lomachenko who remains in his son's corner today.
But there were five medallists at that Games - Denys Berinchyk won silver, Gvozdyk and Taras Shelestyuk took bronze. It was then Lomachenko who burst into the pro game at a million miles per hour, becoming the fastest-ever three-weight world champion, inside 12 fights.
Usyk, just as formidably, became undisputed cruiserweight champion and inaugural World Boxing Super Series winner and is now the WBO mandatory challenger to Anthony Joshua.
But under the radar, Gvozdyk forged a brutal career and became an undefeated light-heavyweight world champion before retiring aged 33 - after his first defeat - earlier this month.
His knockout defeat against Artur Beterbiev in their unification clash was just the second loss in 81 combined fights for Ukraine's five Olympic medallists from 2012 (Lomachenko lost his second pro bout).
Usyk, Lomachenko and Gvozdyk lost just 46 out of a combined 956 amateur bouts.
They have been a wonderfully successful group that are now splintered by Gvozdyk's retirement.
"Gvozdyk and Usyk are definitely different personalities," promoter Alexander Krassyuk told Sky Sports.
"Both are great gentlemen and prominent athletes.
"All people know Gvozdyk as an extremely intelligent man with high-profile analytical skills.
"I had a chance to negotiate the promotional deal with both. Usyk used to make decisions collecting opinions from the advisors around him. Gvozdyk made an impression of a man who takes the final decision himself.
"His manager Egis Klimas told me that Gvozdyk took the decision to switch to commercial activities (private business). I never heard more details.
"Usyk has no plans for retirement at this stage. As long as he stays victorious he will look for higher results.
"Everyone has to finish his career sooner or later. But Usyk wants to make history becoming the only man to be undisputed in two weight divisions."
Gvozdyk may be more single-minded than Usyk in his decision-making but there may be another cause at play.
The Olympic bronze medallist, who signed to Top Rank alongside Lomachenko and is nicknamed 'The Nail', spent his entire pro career in North America and tore his way to the summit of the light-heavyweight division with Mike Tyson's former trainer Teddy Atlas in his corner.
In just his 16th fight he went to Adonis Stevenson's home patch of Quebec and knocked out the former conqueror of Tony Bellew, ending the reign of boxing's long-serving world champion and becoming WBC king.
But Stevenson needed emergency surgery on a brain injury and his career is over.
Less than a year later Gvozdyk's career is also over.
He fought twice more after Stevenson, notably losing a shootout against IBF champion Beterbiev of Russia last October. It was one of the most brutal fights imaginable in boxing, pitting two undefeated, big-punching knockout artists who did not know how to lose against each other.
Gvozdyk was ahead on the scorecards but was floored three times and stopped. He spent two nights in hospital but made a full recovery.
He has not mentioned this as a potential contributor to his retirement. Perhaps, with an Olympic medal and a world championship in tow, it was just the right time to walk away.
He leaves the gloves to his former Ukrainian Olympic team-mates Lomachenko and Usyk who are intent on forging more glory for an already trophy-laden group.