Sir William Osler (1849-1919) and the paternity of William Willoughby Francis (1878-1959): Review of the evidence.

It has been suggested that beneath the sunny personality and enormous productivity of Sir William Osler (1849-1919) lurked a deep sorrow. A longstanding rumor suggests this sorrow was a prolonged affair with an older first cousin, Marian Osler (Bath) Francis (1841-1915), which resulted in Osler's paternity of William Willoughby Francis (1878-1959). Osler treated W.W. Francis like a son. Francis after Osler's death devoted the rest of his life to preserving Osler's memory. Osler's great-great niece Anne Wilkinson (1910-1961) strongly endorses this rumor; Osler scholar George T. Harrell (1908-1999) strongly suggests its truth, while Osler biographer Michael Bliss (1941-2017) dismisses it. Evidence supporting the rumor includes ample opportunities for mating, biographical details, and phenotypic resemblances that are hard to explain otherwise. Barring a DNA-based family study, the truth will probably never be known.