Weddings are often a great first "official outing" for a partner of a royal before they get engaged, so for the BRF i'm still betting on P.Beatrice *with* long-term partner Dave Clark
Maybe for Monaco Pierre Casiraghi with Beatrice Borromeo
I don't think Beatrice and Dave will attend unless they are officially engaged.
Anyway, Beatrice isn't supposed to have a role in the BRF, so I think someone else will attend.
Andrew seems most likely.