Thanks to Lady_Junky for the heads up.
According to IMDB, he is playing "Captain Kidd" https://en.wikipedia.org/wiki/William_Kidd
Just found out that I will be joining the cast of #OnceUponATime!!! Can’t wait for you all to see my character. ;)
— Chad Rook (@ChadRook) November 16, 2017
Wardrobe fitting for #OnceUponATime today. Time to bring this bad boy to life. #StayTuned
— Chad Rook (@ChadRook) November 17, 2017
Reading my script for #OnceUponaTime and WOW.....you fans are in for one hell of an episode.… https://t.co/R2o6uWX98t
— Chad Rook (@ChadRook) November 21, 2017