He shrugged it off, just as he had when reaching yet another landmark that few will ever achieve.
Energumene was beaten but unbowed at Cheltenham, his aversion to the Clarence House Chase, his only defeat over fences last term, again haunting favourite-backers after the race was salvaged from a frosty, abandoned Ascot.
Indeed, this was to be a bittersweet afternoon for Willie Mullins, who batted another accomplishment away, with his usual winsome, win-some-lose-some parlance.
He has been at this game a long time. By his own admission, he knows little else than his preposterous ability to train horses.
To him, the 4,000th winner of his long and distinguished career, achieved when Bronn narrowly justified long odds-on favouritism in the soil.ie Working With Fairyhouse Beginners Chase, was just another victory.
Not that he would not savour it. There were simply bigger fish to fry.
While things did not quite go according to plan at Prestbury Park, with the Queen Mother Champion Chase hero finishing third to to Editeur Du Gite in the Albert Bartlett-sponsored feature, Mullins, underneath his trademark trilby, was still smiling.
"The winner put up a great performance and I'm not going to take that away from him. We weren't able to beat him on the day and just hope it will be a different result the next day for us," he graciously said.
And that is the hallmark of the Closutton handler, who took over from his father, Paddy Mullins, in 1988, having had a hugely successful career as an amateur jockey and also learning more than a few tricks as an assistant to Jim Bolger.
However, he allowed himself a little smile at the milestone, before heaping praise on others, as is his all-too-regular wont.
"I'm delighted," he said, with more than a hint of embarrassment.
"I'm really happy for all the owners we have met throughout the years who have made this possible.
"They are the building blocks we start on, so I'm very lucky with the group of owners I've had over the years, with my family, wife Jackie and (son) Patrick, our staff in the yard who have been with us for years. It is really a family affair."
No question he has stood on the shoulders of his father, who had a legendary career himself, and the 66-year-old has taken tried and trusted methods, honed his experiences and taken this game to another level altogether.
"Everything I learned, I learned from my dad, including patience, which I didn't know I was learning - and didn't want to learn when I was younger, as is the way it is when you are younger," he admitted.
"You don't realise the things you are learning as you are just doing day-to-day stuff until you come across those problems and instances in your life that you think back and go, 'Oh, he would have done this or would have done that'. Then things become simpler and clearer, and you realise why he did those things.
"He was just hugely experienced."
Did he ever think he would be standing in the Cheltenham winner's enclosure, before a Grade One event, looking for winner number 4,001?
"I never dreamt it," he said. "When we were starting off, big jumps trainers had 60 horses, maybe 70. You take the top English trainers at the time, that's the max they had.
"And if someone said to me when I got my licence, I'll give you 60 horses for every year you were going to train for the rest of your life, you'd jump at it.
"The game has just gone bigger. The popularity of jump racing is huge and is growing all the time, and long may it last."
There are no signs he has any thoughts of retirement, and that is a great thing. For not only can you bank on backing WP Mullins runners blind at the March Festival - where he is out on his own as the leading trainer - his son is not yet too keen to have that baton passed to him.
Assistant to his father, Patrick said: "Dad is a huge role model. He taught me everything about riding, all about tactics, how to deal with owners, how to deal with other jockeys. He has all the angles covered and he is always thinking about things that aren't really obvious.
"He learned from his father and built from there.
"I remember, growing up, my memory kicks in when we were second to Noel Meade in the championship and we said, 'We might beat Noel in prize-money, but we'd never beat him in winners'."
Of course, there are always choppy waters to navigate. In 2016, Gigginstown House Stud, owned by Ryanair boss Michael O'Leary, removed 60 horses from the yard, Mullins having put up his training fees for the first time in a decade. If anything, that episode only served to make the operation stronger.
"The big thing was when Gigginstown left, he could have very easily downscaled, but he didn't - he upscaled, and we've more horses now than before Gigginstown left. That is a sign of his ambition," said Mullins junior.
"One day I'll take over, I'm sure. But I'm in no rush and I don't think he is in any rush, either.
"I think he'll train for a long time yet - and that suits me, I'm not in any rush!"
Mullins senior is affable, calm, calculated and competitive. He has an endearing yet sometimes frustrating quality in keeping his cards close to his chest, yet one is left with nothing but admiration for his dominance.
Patrick added: "There is more to training horses than just getting them fit. There is a people side and I think he's very good at it. Some people are good with the people side, but not as good at training, but he's the full package.
"I don't think he is quite as obsessed as maybe Aidan O'Brien, he does have other outlets, he is not one-dimensional."
Mullins senior, a keen Manchester United supporter, likes a round of golf, and by his own admission, is a little more relaxed these days.
"I do tend to try to enjoy things more now," he said. "I find my interest now is downtime, rather than looking for something else to do, just relaxing when we have time off.
"I suppose when you wake up and you hear a horse coughing or bucking, you are living on the job.
"But everything has been great so far, especially when you have someone like Patrick coming up behind."
The dynasty is in safe hands, you can be sure of that. But for now we will raise our glass to the next bucket-load of Mullins Festival winners and doff the trilby in tribute.