Having pondered this for a few days now, my main suspect for who sent Hook the message is Neal.
Phee this is a really good point and I think I might be agreeing. We’ve been speculating on Aurora or Ariel but neither one of them would know Neal’s address. Only a few people were ever in NYC: Rumple, Neal, Henry and Emma. Obviously not Emma and Henry, Rumple is being held by the WW, and Neal.
The only way Aurora or Ariel could send a message like that to Hook would be if one of those two told them everything.
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"He was a lot of things to me" "The only conclusion was love"