One day Rabbi Rene-Samuel Sirat was invited to attend a lecture on the Holocaust, held in the amphitheater of the Sorbonne University in Paris. The speaker, a member of the Academie Francaise, moved the audience when he spoke of a Jewish girl who missed out on a golden opportunity to escape a concentration camp to remain near her parents. Eventually, she was sent to her death along with them.

"Next to me sat Cardinal Lustiger," the former chief rabbi of France recalled. "I glanced at his face and saw tears running down his cheeks. At that moment I knew he was remembering his mother, who suffered a similar fate at the Auschwitz death camp."

Lustiger passed away Monday aged 80. Born Aaron Lustiger, he converted to Catholicism when his Jewish German parents sent him to live with a French Catholic family during the Holocaust. He was ultimately appointed to the Church's most senior positions, and served as archbishop of Paris from 1981 until 2005.

On more than one occasion, Sirat met the cardinal entering Paris' main synagogue. "He would come to say kaddish for his mother," he said.

In 1981, several months after Sirat's appointment as chief rabbi, Jean-Marie Lustiger became archbishop of Paris. The two men became friends. They met frequently, but each time Sirat felt uncomfortable in the presence of the convert who had taken on the mantle of the Catholic church. On the day he was appointed by the Pope, Lustiger declared that he considers himself both a Jew and a Christian, and that he realizes his Judaism by being a devout Christian.

"I could not remain indifferent to these pronouncements," said Sirat, who is currently on a visit to Israel doing research at the Jewish National and University Library. "Together with French rabbis, I harshly criticized the admixture he had made. One of the rabbis wrote in Le Monde that the moment they prove to him that a circle is square, he will accede to the definition that a Jew is the same as a Christian."

Before his appointment in France, Lustiger visited Israel and even contemplated taking a church position here. He knew Hebrew and studied Judaism in depth.

"I was once asked on television what has to happen for Lustiger to be considered Jewish," Sirat said, "so I said that if he returns to the faith, I would even be willing to give up the chief rabbi's seat to him."