QT signal, slot -- how to connect 2 objects that clearly "do not see" each other?

Question

Qt

Good afternoon!
Stalknulsya with such task:
- there is an object A - mainWindow (GUI)
- there is an object B - a stream. its owner - object A
- is object C - another thread. Its owner is object B.
You need to link objects A and C through signals and slots. (roughly speaking, clicking on the button on the GUI - something "calls" in the object C).
While the obvious option is to forward signals and slots from A to C through B, but this is an overhead. To connect a new signal of object A to the slot of object C, 2 more functions are needed: a signal and a slot on object B.
Perhaps there are more rational solutions.