The union of Re and Osiris supposed a challenge to the Ancient Egyptian Art, since new iconography was needed for decorating the tomb walls and the papyri.
From the XVIII Dynasty, some passages of the Book of the Dead were introduced in the royal tombs decoration and that meant to depict moments and gods from the Myth of Osiris into a royal space. However the monarchy was assimilated to the sun god, so some Osirian images suffered a solarization. That forced the ancient Egyptian artist to think of an Osiris-Re iconography.
We saw that in the XVIII Dynasty the figure of Khepri rising up between two images of a kneeling Osiris was the image of the first hour of the Amduat. But the Osirian world was maybe too important in ancient Egyptian belief for reducing it just to this iconography. The conception of the dead god, which resurrected thanks to the action of two women (Isis and Nephthys) was maybe too stablished in the ancient Egyptian thought.
Not for nothing in the XIX Dynasty Sethos I introduced Osirian iconography in royal monuments and he did not forget the two professional mourners…