Of the standard 52 Letters in the English Alphabet, (26 uppercase and 26 lowercase) which was the last letter to be recognised by the symbol which resembles it today? (eg. O is a circle; x is two crossing lines)

The last letter to be added to the English alphabet was the letter J. Similarly to the evolution of U and V, I and J started out as variations of a single letter. Scribes might put a long tail on a final I if there were a few in a row. For example, Henry the Eighth could be written 'Henry viij'. It was up to the scribe to decide which version of the letter he wanted to use.

http://www.bbc.co.uk/dna/h2g2/A2451890