Can you react with a hidden card on the battlefield once Blitzcrank is recalled to hand?

Ruling: You can react to Blitzcrank's hold trigger with a hidden card. However, once Blitzcrank leaves the battlefield, you will lose control of the hidden card and any hidden cards there will go to the trash.

Sequence:

• Blitzcrank is recalled during the beginning step
• Blitzcrank's hold trigger goes on the stack
• You can react with your hidden card at this point
• Once Blitzcrank leaves the battlefield, hidden cards go to the trash

Nuances:

• The hidden card can be used to react before Blitzcrank fully leaves the battlefield
• Loss of control occurs after Blitzcrank leaves, causing hidden cards to go to trash