Will the request go from Client to backend or from frontend to backend?

So i'm trying to make this architecture (using Spring boot) where the frontend is deployed on a public server (on the internet) and the backend server is deployed on a private server in a private network.
The two servers can communicate via a REST API (no worries as to the communication between those 2).

The frontend server is responsible for displaying the pages to say the least.
While the backend server is responsible for the business logic (e.g. authentication).

My question is, if a web page (after being displayed on the client machine) sends a request which is supposed to be treated by the backend server (e.g. http://backend.com/sign-in/), will the request ACTUALLY reach the backend (cause somehow the request is actually sent from the frontend server to the backend server) or will it be blocked cause the backend server is inaccessile (cause the request is sent from the client machine to a server on a private network).

P.S. may the following image help visualize the context.