Complex sentence: Four years after appearing in "Titanic", he joined James Cameron on an expedition to the actual "Titanic", a film about this trip, "Ghosts of the Abyss", was released in 2003.
Split into simpler sentences: Four years after appearing in "Titanic", he joined James Cameron on an expedition to the actual Titanic. A film about this trip, "Ghosts of the Abyss", was released in 2003.