His eldest brother Mieczysław (born in 1887) changed his name to Kochanowski and became composer of dance music before the First World War.

His first widely popular tango was "Złota pantera" (The Gold Panther) to words by Andrzej Włast (1895–1942), premiered in 1929 in Żegiestów.

The song opened all the doors for his subsequent Warsaw career, followed by international tours and concerts in Germany, Austria, and Hungary.

[3] After the invasion of Poland by Nazi Germany he was deported to the Warsaw Ghetto where he played piano at the Splendid Café and the Melody Palace Theatre to survive.

[4] Only the youngest of the Kagan brothers, Alexander (born in 1906), survived the Holocaust as a soldier of the Polish Army in France (1939–40), interned in Switzerland.