There is this from an 1861 letter found in Google Books:
The impression produced here by the death of Count Cavour has been immense—greater, I fancy, than in France, and, if possible, as great as in Italy. This death is the topic of every conversation, the converging point of all minds. The mourning of the English has assumed Biblical proportions: “A Prince has fallen in Israel!”
Louis Blanc, trans. James Hutton, Letters on England, vol. 1, London, Sampson Low, Son, and Marston, 1866.
The letters have been “revised by the author,” so the 1861 date may not be correct. (This is a big problem with volumes of published letters—the wording is often changed by the writer or their family.) But it’s not later than 1866 in any case.