A movie with the hero being the son of a demonic woman and a knights templar.
For some reason, they lived the same age til present time.
This son was left as a baby in a Church, and then was raised by a priest/monk(?).
By the time the hero was a teen, he got hit on the head by a guy due to a girl so his head bled. But his head got healed pretty quickly.
He was eventually discovered by his demonic mother through his blood samples which a doctor analysed, since his love interest got him to a doctor. The doctor reported to the demon mother that he found the guy.
Apparently, the hero never went to a doctor ever.
So eventually he discovered his parentage and met his parents. And then I think in the ending he was the key(?) to using the goblet for the water of life(?) or Jesus' body and blood (?) I think. But somehow I think that in the end, they tricked the mother from using the son so that she could drink from the water of life(?)
I think that the coffin kinda turned blood colored and gooey at the end in order to get the blood, or this could be another movie.
I watched this movie sometime 2007 on HBO.
Added Info The guy was in high school or college, and he got hit on the head when he went to the party of a classmate at the classmate's house.