John Gill Commentary Mark 6:27

"And straightway the king sent forth a soldier of his guard, and commanded to bring his head: and he went and beheaded him in the prison," — Mark 6:27 (ASV)

And immediately the king sent an executioner
(See Gill on Matthew 14:10)

and commanded his head to be brought ;
ordered him to cut off his head in prison, and bring it away forthwith in a charger to him:

and he went and beheaded him in the prison ;
according to his orders.