Since when did the sovereigns begin to be called tsars in the Russian state?

The very first tsar was Ivan 4. His wedding to reign took place in 1547. Thus, the first tsar began to rule in the Russian state. Prior to this, in Russia, princes bore the title of “sovereign”, and even earlier they were called grand princes. True, after the collapse of Kievan Rus, the title of Grand Duke departed and was gradually replaced by “the sovereign of all Russia.”
With the reign of the new tsar, the final formation of Russia as a separate state took place.