Ann Talbot
From Tardis Wiki, the free Doctor Who reference
Ann Talbot was engaged to George Cranleigh, but after his "death" she became the fiancée of his brother Lord Charles Cranleigh in 1925. (DW: Black Orchid)
Ann was the splitting image of Nyssa. At a fancy dress ball at Cranleigh Hall, Ann and Nyssa wore the same clothes to play a trick on the others who couldn't see the difference.