I am researching for my history EE, and I am having troubles with finding the evidence for an event. The event consists in a conversation between the king and Mussolini, which is mentioned in multiple books but without any reference to a primary source, but always to other secondary sources (other historians' books ) or no reference at all. My supervisor was bemoaning this, however it seems fair that there is no "transcript" of a private conversation. Is it common\acceptable? How can I back this event better?
Thank you in advance