The issue is solved through the below code. Thanks to my friend Siva.
Suppose, if the column count is m.
Include Onrowdatabound method with gridviewroweventarguments e.
I took a literal control lit to display my message in the footer.
int m = e.Row.Cells.Count;
for (int i = m - 1; i >= 1; i--)
e.Row.Cells.RemoveAt(i); // which removes the other cells leaving one cell in the row
e.Row.Cells.ColumnSpan = m; // now i'm expanding my row cell with colspan=num of columns
Awesome Coding !! :)