The pope listened intently as a Polish priest who accompanied Lidia Maksymowicz told him of her story. She then rolled up her sleeve to show him the number - 70072. He kissed it and then she hugged him.
Maksymowicz, now believed to be 81, was only two-years old when she and her family were taken from their home in Belarus to the Nazi death camp in German-occupied Poland.
She was put in a children's barracks, where she and others were the subjects of medical experimentation by Doctor Josef Mengele, according to a documentary about her life.
She is the subject of a documentary called "70072: The Girl Who Couldn't Hate. The true story of Lidia Maksymowicz" and meets often with young people in schools.