Sandra Leikanger, 25, and Yair Netanyahu, 23, are both students at the Interdisciplinary Center in Herzliya and met there, the Times of Israel reported. The relationship became public in the Norwegian newspaper Dagen.
Netanyahu reportedly talked about his son's romantic relationship with Leikanger with his Norwegian counterpart, Erna Solberg, at the World Economic Forum in Davos last week.
One of the most outspoken opponents of Yair's relationship with a non-Jew is Hagai Ben-Artzi, his maternal uncle. Ben-Artzi told the ultra-Orthodox website Kikar HaShabbat he would stop the young man from visiting his grandparents' grave if he continues to date Leikanger.
Many Jews, especially the Orthodox, fear intermarriage as a step toward assimilation and away from Judaism. A child must have a Jewish mother to be Jewish.
"Your grandchildren, as you know, will not be Jewish," Bentzi Gopshtain, director of the anti-assimilation group Lehava, warned the elder Netanyahu on Facebook Sunday.
Arye Deri of the ultra-Orthodox Shas Party said the prime minister is a "symbol of the Jewish people." That means, according to Deri, that his son's relationship is not just a private affair.
As often in Israel, the news exposed the divide between the Orthodox and secular Jews.
"It's not fair. You can't expect fairness from those people," Yossi Sarid, a former education minister and leader of a secular party, said. "They don't like non-Jews. They don't like non-Orthodox Jews. They are behaving as fanatics everywhere behave."