selective parent query

My squid proxy has 3 parents:
Twos are for Internet(outside my enterprise).
One is for another division's web server.
The other division's web server is behind the firewall of that division.
That firewall is working also as a proxy for outside clients(inside
my enterprise).

My proxy must be configured to query that proxy as parent only for
that web server.
How to configure for that?
That web server was not registered to DNS and was accessed via IP
address only.

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