You can't be serious (or should I say Sirius). I 'know' you know what it really is, but in case you really don't (which I highly doubt):Quote:The actual Knight Bus seen in the film adaptation [of Harry Potter and the Prisoner of Azkaban] was built by grafting the top deck of a London AEC Regent III RT bus onto the top of another "RT" bus. Both buses were originally built for London Transport; the "RT" was the standard London diesel-powered double-decker bus of which approximately 4,000 were built from 1939 until the mid-1950s (and were used in daily service until 1979). The actual bus used was RT3882 (registration LLU681), with the additional top deck from former RT2240 (registration KGU169). Parts of RT 4497 (OLD 717) were also used. A replica of the Knight Bus sits in front of the London facade at The Wizarding World of Harry Potter in Universal Studios Florida, serving as a stage for a small audience-interactive show with a Stan Shunpike look-alike and a shrunken head.
Magical objects in Harry Potter#Knight Bus