Bulgarian prince and later Tsar Ferdinand I’s gold medal struck to mark the completion of a railway line, €170,000 (£147,825) at Künker.

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He loved to drive locomotives, even though he had no licence to do so, and his reckless driving style was said to have caused the passengers some considerable distress.

When he visited Germany, Emperor Wilhelm II gave strict instructions that Ferdinand was never to be allowed near the locomotive of the trains they travelled on.

One of Ferdinand’s pet projects was the building of a railway line between the central Bulgarian town of Yambol and the Black Sea port of Burgas. The line was completed in 1890, after less than two years.

To commemorate this momentous occasion, a medal was struck in various sizes, in gold, silver and bronze. Only two examples of the largest gold pieces (diameter of 3½in; 9cm) of the series were struck; one for Ferdinand himself, one for his mother.

The latter piece is considered lost but Ferdinand’s medal passed by descent to the royal house of Württemberg.

It became one of the star lots at Künker (25% buyer’s premium) in Osnabrück on November 13-15. It had a face value of 110 Ducats and was dated 14 Mai, 1890. The auction house was expecting €50,000, but in the event the international bidders took the price to €170,000 (£147,825). The buyer remained anonymous.