I am not a researcher of this family, just had ancestors who lived in the area (Lewis, Taylor, Jasper, Hendren).From one of my booklets, "Historical Atlas of Westmoreland County, Virginia" by David Eaton, 1942:
"Capt. Moore Fauntleroy presented a petition in Lancaster County in 1656."Commissioners for the county of Rappahannock (among others) was Col. Moore Fauntleroy.Also mentioned in the militia.
"Moore Fauntleroy lived at Crondell, Richmond County, on the bank of the Rappahannock River, just below Cat Point Creek.His daughter, Mary, married the Rev. Isaac William Giberne, rector of Hanover Parish of King George County." (no year was given, but this sounds like your man)
"Reverend Isaac William Giberne came to Virginia in 1759 and was a minister of Hanover Parish, King George County....he soon married a woman of wealth, a daughter of Colonel Moore Fauntleroy, Mary, who was a widow."