Nick Luck on RTV just spoke to Director of Equine Saftey and Welfare and he said it was a cardio vascular collapse that happened as he came back down the walkway.
He went on to say the vets had checked him (as they do with all the horses) before he started making made his way back down the walkway from the course but then said that the incident happened quickly at the bottom end of the walkway and although the vets got to him quickly they confirmed that he passed very quickly after the incident.
Ultimately he went out on his shield but clearly we all would have much preferred a long and happy retirement for him.
Envoi Allen, thank you for all the wonderful memories you left us with….RIP