The Anak ng Dilim (lit. Son of Darkness) is the prophesized figure to lead the aswangs to victory against the Tagabantay and the Kapatiran and make the aswangs the dominant race over the humans as promised by the aswang goddess Saragnayan to the aswangs. The Anak ng DIlim is the eldest son of Samuel Alejandro, the Haring Aswang. It was known widely that Kael is the prophesized Anak ng Dilim until Juan Dela Cruz is revealed to be the true Anak ng Dilim by Laura to the aswangs. When Samuel Alejandro realized the true identity of Saragnayan, that she is in fact DiwataPeru-ha, he became furious and questioned her what will be the aswangs' real fate. Peru-ha reaffirmed that nothing has changed that the aswang will still rule over the humans but nothing is assured after that. She also said that the Anak ng Dilim will eventually touch the Anito ng Saragnayan and that she will be free from imprisonment.
The Anak ng Dilim is a separate personality within Juan. He was later separated from Juan by Peru-ha.
Peru-ha gave him weapons like Bakal na Krus but it's different,it can changed into three weapons the sword,spear and mace. The Anak ng Dilim impersonated Juan dela Cruz and kidnapped Rosario. He was killed in his final battle against Juan. Or could it be that he goes back within Juan?