The mothers of the three Americans were in Tehran last week see their children. During their visit, they learned that Shane Bauer proposed to Sarah Shourd. He used threads from his shirt to make a ring, and proposed in the prison's exercise area.
The two plan to get married as soon as they're back in the U.S. Fellow prisoner Josh Fattal will be their best man.
The three hikers were taken into custody last July along the border between Iraq and Iran.
Over the weekend, Iran said it would be open to a prisoner swap.