The word "spleened" is spelled with a double "e" after the "n" to indicate the pronunciation /spliːnd/. The IPA phonetic transcription represents the sound of the word as /spliːnd/, with the stress on the first syllable. The extra "e" is added to help maintain the long "e" sound in the word. It is derived from the word "spleen," which is an organ in the body but is also used colloquially to mean anger or irritation.
Deprived of the spleen.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.