I can’t speak to the veracity of this claim, but Crimea might legally be a part of Turkey after declaring its independence — according to the peace treaty signed between Czarist Russia and the Ottoman Empire:
According to the agreement, signed by the the Russian empress Catherine the Great on April 19, 1783, the Crimean peninsula will pass from the Ottoman empire to the Russian empire.
“However, one of the most important points is the clause that stipulates conditions that if the peninsula does not declare its independence then it cannot be transferred to a third party. Otherwise, Crimea must automatically be returned under the aegis of Turkey,” claims the author.
He notes that in 1991, after the collapse of the USSR and the emergence of an independent Ukraine, Turkey has already had the formal right to reclaim Crimea.
There’s an alternative history story to be gotten out of this tidbit.
(H/T Hugo Hackenbush.)