I was at the course and saw this happen. It was a horrible moment. The horse pulled up in the final furlong and was left there stumbling for a while. Then it collapsed with a broken leg and the screens came round.
Most people seemed oblivious to the incident and no comment was made by the course announcer. The vet arrived with the ‘horse ambulance’ and after five minutes the scene was cleared and everyone got back to boozing and betting.
Sad for any horse, but especially for one so young.