|Et regnábunt in sæcula sæculórum.||And they shall reign forever.|
Et regnabunt = and they shall reign, from regno,are, to reign, to rule. Future tense.
in saecula saeculorum = forever. From saeculum,i, an age, an expanse of time. This can literally be translated into the ages of the ages. We use this expression in the Glory Be.