The last letter added to the English alphabet was J
9th January 2024
Originally the same letter as I, J was added to the English Alphabet in 1524 by Gian Giorgio Trissino, an Italian author and grammarian who lived from 1478 to 1550.
Before 1524, the last I in a sequence was written as a J and was interchangeable with the letter I and shared a similar pronunciation.