According to family history, Nathan - Peter Mandelson's great-great-grandfather - was the son of Polish Jew Naphtali Felthusen. Felthusen was a colonel in the 13th Polish Lancers and fought with the Russian 1st Army against Napoleon's invading French forces in 1812.
For his bravery in battle, Felthusen was awarded a coat of arms by the King of Poland, but he was killed in a skirmish as the French retreated across the River Niemen, in modern-day Lithuania, later that year.
Nathan, however, rebelled against the Russian yoke and became involved in the 1825 Decembrist plot to overthrow Tsar Nicholas I. His reward, according to family tradition, was to be declared King of Poland for a day.
When the Tsarist secret police began hunting the plotters, Nathan fled, making his way to England in 1829.
On arrival, he changed his surname to Mandelson to throw Imperialist secret agents off his scent.
Forced to earn his passage to England, Nathan had worked as a baker, a trade in which he made great use of almonds, or 'mandel' in German. He had cooked up a unique family name.
In 1830, Nathan married Phoebe, daughter of Jacob Levy Cohen, of Leicester. The Leicester Cohens were related to a woman named Hannah Cohen who married Nathan Mayer.
Mayer would go on to found a banking dynasty and become the first Lord Rothschild - giving Peter Mandelson a family link to the Rothschild clan.