Maria Theresa (1717-1780) married Francis I, Duke of Lorraine (1708-1765) in 1736. They spent their honeymoon in Florence and in the following year Francis became the Grand Duke of Tuscany on the death of the last Medici Duke. In 1745 he became Holy Roman Emperor.
For other conjoined portraits of Maria Theresa and her husband, see John Winter, Le Statue del Marchese Ginori sculture in porcellana bianca di Doccia (Florence, 2003), pp. 102-105, where he illustrates one in the Museo delle Porcellane di Doccia, Sesto Fiorentino (inv. n. 928), another with a moulded inscription in the Museo Duca di Martina, Naples; and another example with Maria Theresa (only) in the Museo della Porcellane di Doccia.