PSG were pitted against Madrid in Monday's redraw -- after issues with the initial draw, which had paired PSG with Manchester United and Madrid with Benfica, led UEFA to declare it void -- with the two legs to be played on Feb. 15 and March 9.
"Fate is very unpredictable. I'd have liked us to draw another team, but that's how it is," Ramos said on Monday, speaking at the launch of his new gym in Madrid.
"You know the affection and love I have for Real Madrid, that won't ever change. Now I have to face the present. I play for PSG."
Ramos, 35, left Real Madrid in June after 16 years at the club. He had been unable to reach an agreement on a new contract and instead joined PSG as a free agent on a two-year deal.
"It's a mixture of feelings," he said. "I'd have liked not to have had this tie, but on the other hand coming home to the Bernabeu, I had the best years of my life here and not having had a goodbye because of COVID, it's gratifying. I'd have liked it to be another way but that's football. I have to defend my team. I'll go to the death with PSG."
Ramos made his belated PSG debut on Nov. 28, playing 90 minutes in a 3-1 Ligue 1 away win at Saint-Etienne.
It was the first game he had started since May after missing much of 2021 with a series of muscular injuries that followed knee surgery in February.
Speaking on Monday, Ramos admitted that this year had been "a negative part of my life," and criticised what he said had been misinformed speculation about his fitness.
"Honestly I'm very grateful for how [PSG] have treated me," he said.
"The club took a chance on me: Nasser [Al-Khelaifi], Leonardo, [Mauricio] Pochettino... It's a dressing room with so many stars but the reality is different to what it seems like on the outside. They've treated me well."
Ramos described Kylian Mbappe -- who came close to moving in the opposite direction when Real Madrid were willing to pay up to €200 million to sign him last summer -- as "a key piece of the current PSG, and I think the future," and praised former LaLiga rival and now teammate Lionel Messi.
"The relationship is extraordinary," he said. "There's a lot of admiration and respect on both sides. Let's hope we can be decisive in a project like PSG."