Walking on his tiptoes, Ping'an strolls through Beijing's Forbidden City, his suspecting eyes glowing in the dark of the palace that once housed emperors and their concubines.

For years, the cat has roamed the empty lanes of the former royal palace every night after it closes its doors to visitors, in search of his archenemies: mice.

Before being taken in by Shan Jixiang, curator of the Forbidden City - also called the Palace Museum - the animal lived a brutish life beyond the museum's walls, howling and foraging for food among the dustbins during the night.