Distance-Regular Graphs and Halved Graphs

Let G be a bipartite distance-regular graph with bipartition V ( G ) = X ∪ Y . Let V ( G ′) = X and, for x and y in X , let x be adjacent to y in G ′ if and only if x is of distance two from y in G . G ′ is called a halved graph of G , and is distance-regular. This paper addresses the following questions. It is possible that G ′ is one of the known, large-diameter, distance-regular graphs? And if so, what is G ?