Even by soap opera standards, John Castellanos and Mindy Dudek had an extremely unlikely father-daughter arrangement: She saw him in magazines and on the CBS soap The Young and the Restless, where he has played lawyer John Silva since 1989; he didn't know she existed. "I would look at his picture and think things like, 'My cheekbones are kind of like his, and my brows are kind of like his,' " recalls Dudek, who was 11 when she learned Castellanos was her father. "I remember telling people, 'He's my dad.' It was kind of a moot point because they didn't believe me."

At first, neither did Castellanos. In 1999, when he received, mixed in with his fan mail, a letter from ex-flame Gwenda Measel telling him of their daughter's existence along with a letter from Mindy herself, "it was like, 'Is this a hoax?' " he says. Then he looked at the enclosed photo of Mindy. "As soon as I pulled out the picture, my first thought was 'Whoa! Where did someone get an old picture of my mom?' " he recalls. "It's an incredible family resemblance."

Just like that, Castellanos, 47, became a first-time dad to Dudek, now 26. Then seven months ago she gave birth to daughter Gabrielle, and Castellanos took on yet another new role: Grandpa. Father and daughter, who plan to make their first public appearance together at the Daytime Emmys in New York City May 21, are both savoring their budding relationship. "We met as adults, we talk to each other as adults, and we talk about stuff most fathers and daughters never talk about," says Castellanos, who remains philosophical about the years they lost: "I wouldn't have been as ready as I am now for this if I had known about Mindy from the beginning. You can never go back and say, 'What if?' "

Friends of the single Castellanos, who is divorced from producer Rhonda Friedman and has no other children, have marveled at the change in him. "There's just a very positive happiness in him now," says his Y&R costar Peter Bergman. Adds Castellanos, his eyes filling with tears as he gazes at his daughter: "She quickly became a part of me."

Castellanos briefly dated Mindy's mother, whom he'd met in a theater class at Grossmont College in San Diego. But when he transferred to San Diego State University, the pair lost touch and he had no idea she was pregnant. "I suspect that it was because I was very vocal about pursuing a career in acting, and everyone around me knew I wasn't going to be in San Diego long, and that's why she kept me out of the loop," he says of Measel, who is now married to engineer Martin Measel. "But honestly, I've never asked her."

While Castellanos was pursuing his acting career, Mindy was one of four kids being raised in San Diego by Gwenda, now 60, a homemaker, and Martin, 63. When Gwenda told Mindy that Castellanos, not Measel, was her birth father, "I was really freaked out," says Mindy. At the same time, she adds, "I grew up with a lot of love. I was never missing a father."

And yet she couldn't suppress her increasing curiosity about Castellanos. Finally, she and her mom (who declined to speak to PEOPLE for this story) sent those fateful letters. Castellanos wrote back soon after, and at their first father-daughter reunion a few months later, "so many of her features were so familiar," he recalls. "It's like she turns one way and 'Oh! There's my cousin Toni!' " They found they had other similarities as well: "Food preferences, travel. She'll say, 'I have this bad habit,' and I'll say, 'Oops, sorry!' But the biggest one is our sense of humor."

Still, it wasn't until Gabrielle's birth that the pair truly cemented their bond. Now Mindy, who lives in Houston with husband Rob, 33, an office manager, and Castellanos, who lives in Los Angeles, visit each other every two months or so. "I don't want to waste the opportunity again," he says. At the same time, he's waiting to find out how his real-life drama will trickle into his day job. "When our writers hear the whole story, you know this will end up on the show," he says. "I just hope it's in my story line."

Michelle Tauber. Kristin Harmel in Athens

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  • Kristin Harmel.