My feeling is it's Kate. They've done well to divert attention away from her with news on the king.
Alternatively I think Hazza is about to drop another bombshell and they are working out how to best manage it.
They'd have already thought through and planned Andrew being there. Yes one of the children could have had an incident but nanny or granny would have been called on unless quite serious. If Wills was ill I think they'd have just said 'pulled out due to a virus/minor illness'. If it was a security threat then they wouldn't have the Queen (and other royals) in there. Just my thoughts.