A few fans have brought up this quote back from SDCC:
Hook may have a connection to Camelot: “Camelot exists in a parallel timeline,” executive producer Adam Horowitz said. “It’s existed. How we portray it and show you, it’s existed long ago, short ago and maybe in the future. It may have co-existed with [when Hook was in the Royal Navy].”
Source: http://www.ew.com/article/2015/07/11/comic-con-once-upon-time-panel-merida-season-5
We have to question both why it would be important for Hook to have a flashback in 510 during a Camelot themed arc, and why his name ends up on Excalibur. There could be a connection there.
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