It grieved me ___________ my friend’s serious illness.

The blank needs a preposition phrase that correctly expresses being saddened by learning about something.

Option 1 -> hearing regarding -> incorrect; "hearing regarding" is not grammatically correct after "grieved me."

Option 2 -> in hearing -> incorrect; "grieved me in hearing" creates an awkward and ungrammatical construction.

Option 3 -> to hear of -> correct; "grieved me to hear of" is the proper infinitive construction expressing sadness about learning of something.

Option 4 -> to hear regarding -> incorrect; while "to hear" is correct, "regarding" is not the right preposition to use with "hear" in this context.

When something grieves you to hear of, it means you feel deep sadness upon learning about unfortunate news or events. It's the natural emotional response when you discover that something bad has happened to someone you care about, like hearing of a friend's illness or misfortune.