ensuivre

from the Vulgar Latin insequere "to immediately follow, to follow", with a parallel evolution to sequere → suivre. However, the usage tends to reanalyze the verb as en + suivre, which is why we often find il s'en est suivi in the compound tenses where we would theoretically have il s'est ensuivi; this also explains why we rarely find s'ensuivre de quelque chose, the complement introduced by de being felt as redundant with en.