Definition of "highnesse"

I had almoſt forgotten to acquaint your honor, that one major Alford (who was in mr. Love's conſpiracy) was of the graund inqueſt at Saliſbury, and was very zealous in his highneſſe ſervice here, and his good affection and wiſe carriage here, did much advantage the buſſineſe.

1655 April 21, “Mr. Ja. Nutley to ſecreary Thurloe.”, in A Collection of the State Papers of John Thurloe, Eſq; […], volume III, London: […] the Executor of the late Mr. Fletcher Gyles; Thomas Woodward, […] Charles Davis, […], published 1742, page 399