Why are you my Hero (Completed)

The Rebels need to help there new friend who is another Fulcrum. Agent Kallus told the rebels he was Fulcrum and now there also getting help from another Fulcrum. She wants them to do a mission for them and in return they will give the rebels fuel and bombs. Hera thinks they should do it but Ezra keeps saying they shouldn't. He doesn't want to meet the new Fulcrum like they want to meet them in person. They know Kallus well and knows everything about him but he only knows that they exists. How does this Fulcrum know Kallus?
(This has nothing to do with my book Kanan and Ash)