בראשית מח:יט פירוש: רש״י, רשב״ם, אור החיים ורד״ק

ידעתי בני ידעתי I KNOW IT, MY SON, I KNOW that he is the first-born.

ואולם, “but, however.”

וימאן אביו ויאמר, His father refused, saying, etc. The reason the Torah uses the word "he refused," is to indicate that Joseph had taken hold of his father's hand to try and place it on Menashe's head.