Parents of Lewis Green(e) abt 1725-1784)

Has anyone ever found Lewis' parents. I've seen numerous trees listing him as s/o Robert Duff Green (1695-1748) & Eleanor Dunn all with no documentation. I recently found Robt Duff's will which lists his children including 7 sons --but nary any sign of Lewis.
Robt Duff& his wife Eleanor Dunn apparently stayed in the Culpeper Co, VA area although he had extensive land holdings throughout the state. Lewis & his wife Elizabeth Lauderdale show up in the SW VA area near Porter's Fort & Fort Blackmore. There is speculation that he was half-Cherokee & could have been an illegitimate son of Robt Duff.
Any help appreciated. Would like to (1) find my 4g grandfather's roots and (2) correct the numerous possible misconceptions of his descendency from Robt Duff Green.