A spokesperson for Kempton Park said: “All of us at Kempton Park care deeply about the welfare of all racehorses, as do the thousands of racing staff who provide them with world-class levels of care at home every day.
“Our heartfelt condolences are with the connections of all three horses.”
The British Horseracing Authority (BHA) said, external it will analyse each incident in detail through its fatality review process.
“At this stage there does not appear to be any common factor that can be attributed to these incidents, with each of the injuries different in nature and sustained in unique circumstances,” it added.
Briton Nicholls said Kalif Du Berlais had been “travelling beautifully” at Kempton and they had “a lot of faith” the horse could go far.
“He’s won a Grade One and had a big future, there is no doubt about that, but we’re not going to know how big, sadly,” he said.
Harry Derham, who was riding Wertpol, wrote on X, external it had been “an utterly miserable day” and said the three-year-old “was a bright talent who was fresh and happy doing his work every day, often playing around and expressing himself”.
He added: “Racing can at times be a painful sport and today has been a tough day for a number of connections. A day to forget.”