It wasn't rape in the books. It clearly was rape in the show. From the book:
here was no tenderness in the kiss he returned to her, only hunger. Her mouth opened for his tongue. "No," she said weakly when his lips moved down her neck, "not here. The septons . . ."
"The Others can take the septons." He kissed her again, kissed her silent, kissed her until she moaned. Then he knocked the candles aside and lifted her up onto the Mother's altar, pushing up her skirts and the silken shift beneath. She pounded on his chest with feeble fists, murmuring about the risk, the danger, about their father, about the septons, about the wrath of gods. He never heard her. He undid his breeches and climbed up and pushed her bare white legs apart. One hand slid up her thigh and underneath her smallclothes. When he tore them away, he saw that her moon's blood was on her, but it made no difference.
"Hurry," she was whispering now, "quickly, quickly, now, do it now, do me now. Jaime Jaime Jaime." Her hands helped guide him. "Yes,"
Cersei said as he thrust, "my brother, sweet brother, yes, like that, yes, I have you, you're home now, you're home now, you're home." She kissed his ear and stroked his short bristly hair. Jaime lost himself in her flesh. He could feel Cersei's heart beating in time with his own, and the wetness of blood and seed where they were joined.
Made up a name of a king that doesn't exist, Orys the first?