prewarn
verb
pre·warn ˌprē-ˈwȯrn 
variants or pre-warn
prewarned or pre-warned; prewarning or pre-warning
transitive verb
: to warn (someone) beforehand : forewarn
… in 1951, the network began to unravel, and two of its members, Donald Maclean and Guy Burgess, prewarned by fellow conspirators, jumped the night ferry to St.-Malo …
Stephen Koch
Stephen Koch
Word History
First Known Use
circa 1624, in the meaning defined above