User blog comment:Aleksandr the Great/Prothean Squadmate is Officially DLC/@comment-1440333-20120223192334/@comment-1440333-20120223230555

You could find him on Eden Prime as part of the main mission, but perhaps you have to go back to where you found him for his equivalent of a loyalty mission. That could be the From Ashes mission. The very title of it seems to suggest something like that.