Jane Mortimer's sale at Christie's on 25 March 1808 also included as no. 15 'Three (drawings), the original design for the Vortigern and Rowena, ditto for Agincourt, ditto for King John': of the other two oil paintings for which these drawings were for, King John delivering Magna Charta to the Barons was almost certainly exhibited at the Society of Arts in 1776, no. 69, while The Battle of Agincourt was also shown posthumously at the Royal Academy in 1779, no. 203. All three pictures are of the same size and are close in style. This, and the fact that the three preparatory drawings were lotted together in 1808, leads Sunderland to suggest that all were executed in the mid 1770s.

The subject of Vortigern and Rowena appears in John Speed's History of Great Britaine, 1611, and Paul de Rapin-Thoyras's History of England, 1725. Vortigern, Prince of South-East Britain in the mid 5th century A.D. became enamoured of the beautiful Rowena, daughter of the Saxon Hengist, and betrayed the British cause. They are here shown at their first meeting.

Like most of Mortimer's paintings of British historical subjects, with the exception of Magan Carta at Agincourt, this was a relatively rare subject, though it was included in a series of engravings illustrating British History in 1752; Fuseli did a drawing in 1769 (Schiff no. 334) and Angelica Kauffman exhibited a painting at the Royal Academy in 1770