A man in China prepared a romantic proposal for his girlfriend but fell at the final hurdle for the most outrageous reason you could possibly imagine.

The diamond ring he offered her apparently did not fulfill her expectations.

In the video, filmed in Chengdu, Sichuan Province last week, the girl seems very touched at the beginning when the flash-mob starts performing to Bruno Mars' Marry You song, and bursts into tears as the leading man appears with a big bunch of roses.

However, in the end she decided to run away when she was presented with the ring by her knelt-down boyfriend, shocking the spectators who had been supporting the man.

According to local media, the girl was disappointed by the size of the diamond on the ring which was reportedly "less than a carat".