Singer-songwriter Alanis Morissette learned about a painful chapter in her Jewish family’s past during last night’s season premiere of Finding Your Roots, an American documentary series that explores celebrities’ genealogy.

Thanks to records that the Finding Your Roots team discovered at Yad Vashem, Morissette learned that both of her grandfather’s siblings Gyorgy and Sandor Feuerstein died in Soviet slave labour camps during the Holocaust and that her grandfather, Imre Feuerstein, made inquiries to the Red Cross to find them.

The seven-time Grammy Award winner and rock sensation of the 90s told Finding Your Roots host and Harvard University history professor Henry Louis Gates Jr. that she came late to her Judaism, having only learned about her family’s Jewish origins when she was in her 20s.

Born in Canada to a Hungarian mother whose parents were both Holocaust survivors, Morissette, 49, explained that her mother and grandmother’s decision to hide the family’s Jewishness was probably due to “a terror that is in their bones”: “They were being protective of us and just not wanting antisemitism.”

But Morissette, who was raised Catholic, did not know the extent of the family’s trauma. Gates explained that her grandfather spent years wondering whether his brothers were alive or dead. In archives of the Red Cross, Gates revealed that Imre Feuerstein made inquiries after the war in the hope of finding one of his brothers.

According to the archives at Yad Vashem, both brothers were sent to labour camps in Russia, where almost half of the prisoners were Hungarian Jews, and both died there.

“It’s unfathomable for me,” Morissette said of imagining what her uncles had to endure.

Morissette is the latest in a string of celebrities who have explored their Jewish heritage on Finding Your Roots, which just entered its 10th season. Past guests, including Paul Rudd, Dustin Hoffman and Scarlett Johansson, made discoveries about their Jewish lineage through the docuseries.

Later in the season, the show is scheduled to host Jewish actors and comedians Lena Dunham, Iliza Shlesinger, and Michael Douglas.