Burke, J.B. (1852). "Henry de Percy, 3rd Lord Percy of Alnwick." A Genealogical and Heraldic Dictionary of the Peerage and Baronetage of the British Empire, (14th ed, pp.746). London: Colburn & Co. Google Books.
Brydges, E. (1812). "Percy, Duke of Northumberland." Collins's Peerage of England Genealogical, Biographical, and Historical, (Vol. II, pp.217-366). London: F.C. and J. Rivington, Otridge and Son. Print.
It may be possible to confirm family relationships with Henry V by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree: