What is ironic about the ending of the poem "richard cory" by edwin arlington robinson?

The irony about the ending of the poem "Richard Cory" by Edwin Arlington Robinson is that Richard Cory, the person being talked about in the poem, who was envied by many because of his wealth and class, committed suicide. It was a shocking ending because no one thought he would end his own life in spite his possessions of brilliance. 

alone =having no one else present.