Anne had been suggested for the role and that Philip supported that.
Just days ago I saw a headline about Charles not having Anne in the slimmed down family when he is monarch, but I cannot find it again.
And we have since read of William for the role. And Harry will not be there for the ceremony at the Cenotaph.
I think quite a bit of deliberating is going on, to get it clarified ahead of time, so as not to overshadow the solemnity of what is a top day in the royal year.