ことを (nominalized object)

The pattern [clause]+ことを, nominalizing a clause with こと and marking it as the direct object of the wrapping verb. Used with verbs that take whole propositions as their objects: ~ことを思い出す ('remember that'), ~ことを後悔する ('regret that'), ~ことを恐れる ('fear that'), ~ことを発表する ('announce that'), ~ことを忘れる ('forget that'). Compared to のを, ことを is more abstract/formal and suits 'fact / matter' readings rather than concrete events.