Would have been 12, but they didn’t award posthumously at the time.
From Wiki: In 1879 there was no provision for the posthumous granting of the Victoria Cross, and so it could not be awarded to anyone who had died in performing an act of bravery. In light of this, an unofficial “twelfth VC” may be added to those listed: Private Joseph Williams, B Coy, 2nd/24th Foot, who was killed during the fight in the hospital and for whom it was mentioned in despatches that “had he lived he would have been recommended for the Victoria Cross”.
Thanks