Star Trek: Deep Space Nine S05 E19 Ties of Blood and Water

"At the edge of the Final Frontier, the Universe's greatest mystery is about to unfold."

Stardate: 50712.2. When a Cardassian official that thinks of Kira as his daughter is dying, he agrees to reveal all he knows to her. But the experience dredges up Kira's memories of her own father's death.