Mega Charizard ex, Mega Dragonite ex, and Oricorio ex were just revealed during the closing ceremony of Worlds! They will appear in future English sets.  We don't have the set names yet, but will report when they are available. 

Also revealed is a new type of secret rare card for Mega Pokémon named "MA," or "Mega Attack" rare.

Like the original Mega Pokémon, this rarity will have the Pokémon's attack name written over the artwork. In English they will show the Japanese names while in Japanese they will show the English names.

Mega Charizard ex will debut in Japan's Inferno X, which releases in Japan on September 26th. In English it will release in November's Phantasmal Flames along with Mega Gengar ex and Mega Diancie ex.

Mega Dragonite ex will debut in Japan's Mega Dream ex in November.