Which preposition to use with forewarns

of Occurrences 7%

I cannot forbear to observe, in this place, that, as it is of no advantage to mankind to be forewarned of inevitable and insurmountable misfortunes, the author, probably, intended to hint to his countrymen the proper remedies for the evils he describes.

as Occurrences 2%

While you are thus forewarned as to your situation, keep a prudent eye on your affairs."

by Occurrences 1%

Only a Farfan escaped, not without suspicion of forewarning by the rebels.

Which preposition to use with  forewarns