Prince Leopold of Saxe-Coburg and Gotha (Kohary linie) [1878-1916] was the eldest child, only son, of Prince Philipp of Saxe-Coburg and Gotha and his wife, née Princess Louise of Belgium, herslef the eldest daughter of King Leopold II of the Belgians.
Prince Philipp's father, Prince August (1818-1881) was a first cousin of King Leopold II. Both August and Leopold II were also first cousins to Queen Victoria and Prince Albert, all four being grandchildren of Duke Franz Friedrich Anton of Saxe-Saalfeld-Coburg and his second wife, the former Countess Augusta of Reuß-Ebersdorf.
Furthermore, Philipp and Lepold II were also both granbdsons of King Louis Philippe of the French through their mothers: Queen Louise Marie of Belgium and Princess Clementine of Saxe-Coburg and Gotha - both born members of the Orléans family.
As for Prince Leopold he did indeed die from wounds suffered after his mistress attacked him, first shotting him and then throwing acid at him. However, and contrary to popular belief, Leopold did not die after the attack, as in fact he survived several months of terrible agony. It seems that he broke off his relationship with this woman for as the eldest of his line and heir to the vast Kohary inheritance in the Austro-Hungarian Empire, Leopold needed to produce a legitimate heir from an equal marriage. The lady in question did not like this and took mad action against her paramour.
Leopold also had a really bad relationship with his mother Louise, as he felt the full brunt of her scandals and infidelities. In her own memoirs, Louise Coburg expresses almost no regret for her son's fate...all too sad really.
Arturo Beéche