I doubt Louis will be there for the whole shebang. I suspect he'll be brought to the Abbey at a certain point by his nanny and then join his parents and siblings as they process out. I suspect that plan may have been suggested to the Sussexes for Archie, at least (Lili is just way too young, period) if they attend and Meghan's narcissism has rejected it because of the need to be front and center.
I've read that people are pitching fits because Camilla's grandchildren are all invited, but not Archie and Lili. Apparently it hasn't occurred to anyone that Camilla's grands are all teenagers who can behave themselves.
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