As posted by Pavanne in another thread, in the 17th c. versions of Child 81, and the one in Pepys Ballads I, the characters are Little Mousgrave (Musgrave, Musgrove) and Lady Barnet. The lord was feasting with friends; no kings, queens or Whitehall are mentioned.

Child, the English and Scottish Popular ballads, quotes Percy: "This ballad is ancient, and has been popular; we find it quoted in many old plays." He mentioned one of about 1611.
It is likely that the song originated in the theatre; the characters entirely fictional.