'Ё' is the youngest letter in the Russian alphabet

The letter 'Ё' appeared in the Russian language at the very end of the 18th century, but it was only officially approved in 1942. Before that, it was simply considered a variant of the letter 'E'. 

However, it is still not uncommon to omit the umlaut above this letter in writing. The correct pronunciation should be clear from the context, although it can be difficult for students of Russian. For example, 'поем' [“I'm going to eat”] and 'поём' [”we sing"].