The Tudors, starring Jonathan Rhys Meyers as King Henry VIII, has been one of the most successful shows for the US giant TV cable network Showtime, drawing more than a million viewers per episode.
It won Rhys Meyers and the series Golden Globe nominations, and for two consecutive seasons, Joan Bergin's costumes won Emmys.
Filming the latest series at the 800-year-old castle is expected to bring a major boost to local tourism in the north Co Dublin town.
A chapel in the castle, which was once the residence of the Archbishop of Dublin, has been restored to its former glory and was officially opened last week.
Work on the rest of the complex has been on-going since 1995.
Earlier this year, Showtime announced it had renewed The Tudors show for a fourth and final season, with 10 episodes due to be broadcast in spring.
The premiere of the show in April 2007 was the highest-rated Showtime series debut in three years.
The show, which is filmed in Ireland, was then renewed for a second season, and in that month the BBC announced it had acquired exclusive British broadcast rights for the series, which began airing there in October 2007.
By season three, it had become one of Showtime's most popular series.
Season four will be written by series creator and executive producer Michael Hirst.
The final season will consist of 10, one-hour episodes and centre on King Henry's tumultuous relationships with his last two wives, Catherine Howard and Catherine Parr, and his final descent into madness.