We are just learning fresh news about research on King Tut's mummy, in advance of tomorrow's publication in the American Medical Journal of the results of the most recent DNA and other tests. Over the years, there have been many different theories, but now we can scientifically prove what killed the Boy King, his parentage, and other health conditions affecting him at the time of his death.
Early Research
KV62 - Tut's tomb - was discovered by Howard Carter in 1922. Multiple attempts at proving kinship between various royal mummies have been made since then, including tests by Connolly (1976), Flaherty (1984) and Harrison (1969). In the case of Tutankhamun and Smenkhare, these tests have included estimates of both mummies' blood groups in order to compare them.
Both mummies share the same rare blood type (group A2, and both with the serum antigen MN), suggesting close consanguinity.