Sons of Fortune - Jeffrey Archer

In the late 1940's in Hartford, Connecticut a set of twins is parted at birth. Nat Cartwright goes home with his parents, a schoolteacher and an insurance salesman. But his twin brother is to begin his days as Fletcher Andrew Davenport, the only son of a multi-millionaire and his society wife.
During the years that follow, the two brothers grow up unaware of each other's existence. Nat leaves college at the University of Connecticut to serve in Vietnam. He returns a war hero, finishes school and becomes a successful banker. Fletcher, meanwhile, has graduated from Yale University and distinguishes himself as a criminal defense lawyer before he is elected to the Senate.