Context:

Referenced multiple times throughout the episode. First mentioned as someone 'who love[s] Napoleon,' then cited directly regarding Josephine's possible PTSD ('Andrew Roberts says he thinks she was suffering... post-traumatic stress disorder'), and again when discussing intimate details ('Andrew Roberts discusses, says he doesn't know what it is, which is called the zigzags'). These references are to Roberts' Napoleon biography.

Context:

Explicitly referenced as 'Andrew Roberts in his biography' when discussing the detail about Napoleon noting Saint Helena in his school exercise book. This is Roberts' Napoleon biography.