  A graph is said to be diameter-$k$-critical if its diameter is $k$ and
removal of any of its edges increases its diameter. A beautiful conjecture by
Murty and Simon, says that every diameter-2-critical graph of order $n$ has at
most $\lfloor n^2/4\rfloor$ edges and equality holds only for $K_{\lceil n/2
\rceil,\lfloor n/2 \rfloor }$. Haynes et al. proved that the conjecture is true
for $\Delta\geq 0.7n$. They also proved that for $n>2000$, if $\Delta \geq
0.6789n$ then the conjecture is true. We will improve this bound by showing
that the conjecture is true for every $n$ if $\Delta\geq\ 0.676n$.
