If one counts ten days from 11.4, the tenth day is 11.13.2020, a Friday, the sum of the digits of which is 10.
The only interesting historical event I can find tied to that date is the St. Brice’s Day massacre in 1002 when Æthelred II, The Unready, killed all the Danes in England.
who ever said you can never get rid of the Dane?
That is Friday the 13th.