Johann Joseph von Semlin (born Mostafa Ali Mirza Khan, Persian: مصطفی علی میرزا خان‎; 1736–1824) was the reputed son of Nader Shah.

After his father's murder, a loyalist brought Ali Mirza Khan to Maria Theresa in Vienna, then Austrian Empire, who named him "Johann Joseph Freiherr von Semlin".

On completing his education at a Viennese military school, Von Semlin joined the Austrian army, rising after a few years to the rank of Commander.

An ambassador of Napoleon requested Von Semlin to attempt to take the throne of Iran, offering him military support.

Even if I have any rights to become king of Iran, I cede them to Francis II, Holy Roman Emperor, who supported me to this age.