There is a certain pleasure akin to sadness [...].
Esse aliquam cognatam tristitiae voluptatem [...].
Notes from Wikiquote
Attributed to Metrodorus by Seneca, Epistulae morales ad Lucilium, XVI, 99, 25, as translated by Richard Mott Gummere, Moral letters to Lucilius, Loeb Classical, 1925.