Game of Thrones Season 7 will likely bring back long-lost character, Gendry. This rumor surfaced when Joe Dempsie was spotted at Belfast airport where season 7 is being filmed.
The last time Gendry was seen in the series was in season 3 when Davos rescued him from Milsandre. Without Davos, he and his blood would have been used for blood magic and eliminate all enemies of Stannis. Davos guided him to a small boat to leave Dragonstone and head back to King's Landing. However, Gendry admitted he does not know how to swim so no one really knows if he has survived his journey back home.
Although seeing Gendry played by Joe Dempsie back in Belfast, doesn't really mean he is back. No official statement has been given by the show and previous stars of the show are known to visit the set and meet with their old friends such as Sibel Kekilli (Shae).
But if Gendry does come back, he can question Cersei right to the throne since he is related to Robert Baratheon by blood. The last two kings, Tommen and Joffrey, were revealed to be the son of Jaime, Cersei's brother, so they don't really have any right to it.
In addition, Arya decided to go back to Westeros that could possibly lead her to find her old friend Gendry. If this happens, it will definitely add much excitement to the series and affect how the other kingdoms will react.
Game of Thrones Season 7 is said to premiere in the middle of 2017 with only 7 episodes, compared to 10 of its previous seasons. It was ordered just last April 21, 2016, three days before season 6's premiere. It is based on George R. R. Martin's "A Song of Ice and Fire" series but also takes adaptation from "A Dream of Spring" and "The Winds of Winter".