The holiday was established in 1845 to commemorate the birthday of Queen Victoria (the British monarch who later gave royal assent to Confederation). But it was not until 1901, the year of Victoria’s death, that the holiday officially became known as Victoria Day. Since that time, the holiday has commemorated the birthday of the current monarch, as well. https://www.noslangues-ourlanguages.gc.ca/fr/writing-tips-plus/victoria-day-fete-de-la-reine.html