Apponius affirms the procession of the Holy Spirit from both the Father and the Son, and he doesn’t seem to think it’s even controversial. He mentions it in Book 3, in the context of a lot of other stuff, in the middle of an explanation of Songs 2:4 (“He brought me into his wine cellar, and he set in order the charity in me.”)
So then we get through the wine cellar and get to how charity can be set in order. At this point he starts talking about an “order of charity” [ordine charitatis] as relating to what things need to be taught and believed, and finally he starts talking about the Trinity. He talks about the Father as being the Voice in which the Son always is the Word. And then he talks about the Holy Spirit as third in the order of love within the Trinity. And then, he comments:
“Qui Spiritus vera ratione de Voce et Verbo, de Patre et Filio, procedere comprobatur….”
(“Which Breath is thoroughly proved by true reason to proceed from the Voice and the Word, from the Father and the Son….”)
Apponius gets all sorts of different datings from different scholars, but he’s obviously from long before the Filioque clause was first used in the West. So this is interesting.
Apponius talks a fair amount about the Trinity, in passing, in his Commentary on the Song of Songs. I was just startled by him touching upon this doctrine so casually.