Notice the 13th-century version is by Saint Thomas Aquinas, not Bishop Fortunatus.
In addition to providing the Latin version with accent marks, the Saint Jean de Brébeuf Hymnal commissioned English translations from Latin scholars to help congregations appreciate these ancient prayers. Until the Brébeuf Hymnal appeared in 2018, literal translations for many of these hymns had never been made.
The final two verses are “TANTUM ERGO SACRAMENTUM.”