Twin Dragons is a 1992 Jackie Chan film where he plays the parts of 2 twins who were separated at birth and ended up with very different upbringings - one (John Ma) became a famous classical pianist whilst the other (Boomer) became a common crook.
As is inevitable in such a situation when Ma visits Hong Kong he and Boomer are mixed up with each other and are forced to assume each other's identity. Boomer eventually has to come to the rescue of Ma when he gets himself stuck in the middle of a gang war.
See also