The Third Corvinus Son is the unnamed brother of Marcus and William Corvinus and the son of Helena and Alexander Corvinus. He is the only son of Corvinus to carry the Corvinus Strain in its dormant form. The third son died as a mortal; however, the dormant gene lying within him would have allowed him to become Immortal had the gene been activated.
In Underworld, the Lycans discover that the latent Corvinus Strain has been passed down in the bloodline of the third son, making it possible for a direct descendant to become infected with both the Lycan and Vampire bloodlines. The Lycans' search for a descendant of the third Corvinus son leads to the creation of the first Hybrid.