Which of these four cities is the most populous?

Here are the details on the four answer options, giving the official population figures (and dates):

Istanbul, Turkey, 15,462,452 (31 December 2020)

Moscow, Russia. 12,195,221 (1 January 2019)

London, United Kingdom, 9,126,366 (31 December 2018)

Berlin, Germany, 3,748,148 (31 December 2018)

Istanbul, formerly known as Byzantium and then as Constantinople, is Turkey’s economic, cultural and historic centre. It is easily the largest city in Turkey: its 15 million residents, comprises 19% of the country’s total population. It is the most populous city in Europe, and the world's fifteenth-largest city.

In 1923, after the Turkish War of Independence, Ankara replaced the city as the capital of the newly formed Republic of Turkey. In 1930, the city's name was officially changed from Constantinople to Istanbul, a word that Greek speakers had used for the city since the eleventh century.

Over 13.4 million foreign visitors came to Istanbul in 2018, eight years after it was named a European Capital of Culture, making it the world's eighth most visited city.