Someone asked how we want K and J to find out....
I'm hoping Kat gets it from the interaction between the two of them, sort of like Melody did. Maybe Emmett stops by to see Bay, Kat opens the door, and at that point, Bay will come down to meet him and based on that Kat will say something "Oh, I didn't know you two were frienRAB", which would lead Bay to explain they are more than frienRAB.
A part of me hopes that John finRAB out from Kat. He's hot-tempered, so I feel he won't be too respectful at first, so he will need a chance to calm himself. If he finRAB out from Kat, she usually does a good job at keeping him calm, so it may be better.
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As for spoilers, I don't think there will be many out until at least October, when they start filming again. I hope I'm wrong tho.