Madrid were beaten 3-0 by PSG in September in a disastrous opening Group A game that Mbappe missed through injury.
"I've known him for a long time" Zidane told a news conference ahead of the game at the Bernabeu. "I've been in love with him for a long time, but as a person first.
"He came here for a trial a long time ago. Tomorrow he comes here as an opponent."
He added: "What's important to me is what we are going to do. We know the player he is and his importance to his team. We have to be ready."
PSG boss Thomas Tuchel, meanwhile, questioned Zidane's feelings for his star player and suggested that love is not always reciprocated.
"I do not know in what way or how much Zinedine Zidane is in love with Kylian," Tuchel said. "But the most important thing is that he is our player. Often, we love lots of things that we ultimately cannot have."
Tuchel added that Zidane's platitudes didn't cause him any concern.
"I was in Geneva with Zidane two weeks ago. We did not discuss Kylian. If a question is asked about Kylian, he is French -- what can he say? Everyone knows he loves Kylian, like many coaches. I am not upset," he said.
"Kylian is our player. We are trying to create a team with him. I do not want to consider Kylian departing anytime soon."
Madrid have got their Champions League campaign back on track since that Paris defeat with back-to-back wins against Galatasaray, including a 6-0 thrashing at the Bernabeu.
"It is the most important game of the season because it's the next game and against a very good opponent" Zidane said. "We need heart, head and above all football.
"If we're good with the ball, that's the important thing."
Tuesday's game will see more scrutiny for Gareth Bale, who was loudly whistled by the Bernabeu crowd on Saturday in his first appearance since the infamous "Wales. Golf. Madrid. In that order" flag celebration.
"We want him to help us win" goalkeeper Thibaut Courtois said on Monday. "It was the euphoria of the moment and it's been made bigger than it is.
"I know Gareth, he's a great professional. You saw how he played the other day. He wouldn't have played like that if he wasn't committed."
PSG are top of Group A on 12 points guaranteed qualification to the Champions League knockout phase. Madrid are second on seven points -- five ahead of Club Brugge -- with two matches left to play.
Zidane's side visit the Belgians, who led 2-0 at the Bernabeu in October in a game that ended 2-2, in their final group game.