Who is the murderer in 'Evil under the sun'?

In Agatha Christie's "Evil Under the Sun," the murderer is revealed to be Arlena Stuart's husband, Simon Doyle. He orchestrates the murder to eliminate her and be free to pursue a relationship with his lover, who is also involved in the plot. The story unfolds through the investigation led by Hercule Poirot, who uncovers the layers of deception surrounding the crime.