My first thought was against the last person you mentioned: Henry... but then, Robert (for Walpole) even though he was never named as 'Prime Minister' (and at the time when he was First Lord of the Treasury, 'PM' was a derisory term used by the opposition to illustrate the incompetence of the rest of the cabinet, but never mind). The first de jure Prime Minister was Henry Campbell-Bannerman.
As for King of Italy... depends what you mean. But I don't recall any King of Italy being called 'Robert'. And it depends on the definition of 'Italy', because there were Kings of the Sicilies, Lombards, Naples, Savoy, Kings in Italy and Kings of HRE Italy, but the only proper Kings of Italy who could claim Kingship of the entire peninsular were Victor Immanuels II & III and Umbertos I & II.
The more you know...
Anyway, OT: s'OK... I prefer my nickname: Fatso... *shrug*