It's not that hard when the timing between raphiel's death & raphiel jr's birth were not match. Raphiel died way before the son was born. Beside, raphiel jr also came across aeroc when he was a kid.. or maybe he met with hugo the butler. Hugo will automatically recognised raphiel since he's a carbon copy of aeroc.. whatever it is, I love that the son knew the truth about his mother..

Wait .. how did his son know about what happened .. and I didn’t understand the chapter like did the son know that his mother is not Raph but Aeroc