According to the Grey family, Earl Grey tea was specially blended by a Chinese mandarin for Lord Grey, to suit the water at Howick Hall, the family seat in Northumberland, using bergamot in particular to offset the preponderance of lime
in the local water. Lady Grey used it to entertain in London as a
political hostess, and it proved so popular that she was asked if it
could be sold to others, which is how Twinings came to market it as a
brand.
The Earl Grey blend is named after 2nd Earl Grey, British Prime Minister in the 1830s and author of the Reform Bill of 1832, who reputedly received a gift, probably a diplomatic perquisite, of tea flavoured with bergamot oil, taken from bergamot, a citrus fruit typical of Southeast Asia and grown commercially in Italy. According to one legend, a grateful Chinese mandarin whose son was rescued from drowning by one of Lord Grey's men first presented the blend to the Earl in 1803. The tale has no basis in fact, as Lord Grey never set foot in China and the use of bergamot oil to scent tea was then unknown in China. However, this tale is subsequently told (and slightly corrected) on the Twinings website, as "having been presented by an envoy on his return from China"
Source & More Information: Wikipedia, http://en.wikipedia.org/wiki/Earl_Grey_tea