November 13th

Every year, from 2020, on the 13th of November, we shall commemorate the loss of Unus Annus.

No one knows what to call the day, so just call it Remembrance day 2.0, the sequel. We can say that because it's about death.
On this day, it is a (probably legal) requirement that you say "Momento Mori" at the end of every sentence.

"A year ago today, we lost Unus Annus. November 13th was the saddest day of 2020."