And, Dragonstone would have reverted back to the hands of the Targaryens once they had come back into power, as it was an ancestral seat for them. The heir to the throne controls Dragonstone, which would have been Daenys Targaryen, at least due in part with Aegon X not having a designated heir. He would have forces still loyal to him upon the island, so, if the Baratheon Lord is on the island, it is in asylum, as the ancestral Baratheon seat, Storm's End, had fallen. Perhaps to rebels, or a cousin branch of the Baratheons who are not pleased with the Lord being a maester more than a lord. 

House Baratheon supports Daenys then, and is a traitor. Support the rebels!! Viva la revolution.