The seven-year-old was pulled up sharply by Jamie Spencer with around two furlongs to run in the tote Foundation Stakes and was taken for X-Rays.
Menuisier later confirmed the son of Exchange Rate could not be saved.
I can’t really describe how painful it is to have to report the loss of our beloved THUNDERING BLUE. He lived his Life like a warrior and fought his last battle bravely too. He will be remembered as the horse of a lifetime and a great friend. We LOVE you forever. @KimJohnstone6 pic.twitter.com/RKyKFItSes— David Menuisier (@DavidMenuisier) September 23, 2020
He tweeted: “I can’t really describe how painful it is to have to report the loss of our beloved Thundering Blue. He lived his life like a warrior and fought his last battle bravely too.
“He will be remembered as the horse of a lifetime and a great friend. We LOVE you forever.”
Thundering Blue won six of his 29 races, including the Group Two York Stakes and Group Three Stockholm Cup, was twice placed in Group One company and won over £460,000 in prize money.
Relive Thundering Blue's victory in the 2018 Sky Bet York Stakes
Dropped out early by Levey, she was one of five in a line with a furlong to run as the Godolphin pair of High End and Mythical Magic took on Desert Icon and Oriental Mystique.
Anna Nerium came widest and fastest of all, going on to win at 10-1 – by a length, with High End in second.
Levey told Racing TV: “There was never a doubt about the trip in the end.
“I’m delighted for Mrs McCreery (owner), who has been absolutely brilliant to me ever since I started with the Hannons. It’s nice to win a big race every year with horses like Billesdon Brook, too.
“Although she’s won in the height of summer before, it’s never been her type of ground. Coming here with the rain today, I was actually a little bit confident that she’d run a big race.
“I’m of the belief that if you have a keen horse stepping up in trip, there’s every reason to drop out the back, but you still have to run the same distance. She’s laid back, though, so it was straightforward in that regard.”
Sean Levey reflects on Anna Nerium's victory
Levey is looking forward to riding Happy Romance in the Cheveley Park Stakes on Saturday – although he fears soft ground.
“She’s well worth a crack at a Group One, but I’d fear the rain – realistically I don’t think she’d like soft ground,” he said.
“It has been on the easy side the last twice – but stepping up to that class, you want everything in your favour, and I think that would be quick ground.
“She hasn’t missed many dances this year, but she’s only been beaten twice. She’s got a great mentality and never gives absolutely everything, which is giving her longevity.”
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