Moehat, the Kauto Star remounting incident where he was injured was in a novice chase on 31/1/2005.
Best Mate died in the Haldon Gold Cup on 1/11/2005. You probably have that race in mind as it is where Kauto Star made his comeback from the injury, finishing second to Monkerhostin.
I had forgotten that Best Mate and Kauto Star ever ran in the same race. What a shame it ended so sadly.