The True Tragedy of Richard III a source for his play, though the majority tend to favour this judgement. Geoffrey Bullough treats "The True Tragedy" as a "probable source" for "Richard III", citing several commonalities (as when, in both plays, Richard calls for a horse on Bosworth Field, yet refuses to flee the battle) — though Bullough admits that the nature of the plays' relationship is "not clear." The uncertainty in dating has allowed a few commentators to propose a reversed priority, and to argue that the author (or reviser) of "The True Tragedy" may have borrowed from Shakespeare's play. Shakespeare appears to have known of
Richard III of England same direct maternal line. Joy Ibsen's mitochondrial DNA was tested and belongs to mitochondrial DNA haplogroup J, which by deduction, should also be the mitochondrial DNA haplogroup of Richard III. Joy Ibsen died in 2008. Her son Michael Ibsen gave a mouth-swab sample to the research team on 24 August 2012. His mitochondrial DNA passed down the direct maternal line was compared to samples from the human remains found at the excavation site and used to identify King Richard. On 4 February 2013, the University of Leicester confirmed that the skeleton was beyond reasonable doubt that of King Richard III.