Thomas Percy's version includes the lines (spoken by Lord Barnard):

"For I have slaine the fairest sir knighte,
That ever rode on a steede;"

That at least seems pretty unambiguous.

Percy also states that the ballad:

"is ancient, and has been popular; we find it quoted in many old
plays. See Beaum. and Fletcher's ' Knight of the Burning Pestle,' 4to. 1613"

which places it earlier than the ECW.