After the Return of the Jedi, Luke senses that he was conned by a fake Vader whom he thought was his father. Vader actually had a secret brother. So, because they were brothers, Luke could not tell the difference between the two. After the real Vader discovered that he had a son, he had a mid-life crisis, was going all over looking for answers. He even fought the Emperor out of anger, because the Emperor never told Vader that he was a father, that he had a son. Vader eventually went deep into space to search for answers. Luckily, the Emperor was able to get his brother to take his spot. The Emperor was only aware of the creation of Anakin, but the master of the Emperor failed to tell him that an identical twin was also created on another planet far away. But after Vader had his temper tantrum after A New Hope, & ran off, the Emperor started seeing visions or feelings of the force or murmurs from ancient sith that led him to discover the brother of Vader similar to how Darth Maul has a brother. Star Wars VII takes place thirty or more years after the Return of the Jedi, & this will be one family reunion that you do not want to miss.