The first English civil war started in 1642, Charles I was beheaded in 1649 and his son Charles II would not be king in England before 1660 at the restoration.
So in 1653, a 'royalist' was against the 'Commonwealth', which was the anti-monarchist side.
So in 1653, a 'royalist' was against the 'Commonwealth', which was the anti-monarchist side.