I haven't been following any rumours about the affair (not a royal fan at all but the Harry spat intrigues me)...
Well I was thinking maybe it's like a public olive branch since a personal message to Kate may not be well received, but just to let W&K know they do wish well and are there for her.
Probably giving them way too much credit. But I feel like after the cancer news, Harry at least must feel sad and perhaps even guilty given how close the trio seemed to be at one point doing Invictus. Harry seemed to be thriving then too.
Not to push the "vixen woman, innocent man" narrative but it seems Meghan does bring the worst out of him (or at least they bring the worst out of each other).
Harry has always seemed impressionable, I feel like Kate was a bit of a mother/older sister figure to him during the trio days and now Meghan's taken that role.
He's been viewing Kate through a lens of resentment since he met Meghan, whereas they were all close before. Maybe the latest news will give him a more objective view/appreciation of his SIL... People are like that, always need a wake-up call