Andrew McCarthy and Son Sam on What They Learned From Each Other on 500-Mile Walk Through Spain (Exclusive)

Andrew McCarthy and his actor son, Sam, embarked on a five-week journey across Spain's Camino de Santiago, which is chronicled in McCarthy's latest memoir, Walking With Sam: A Father, a Son and Five Hundred Miles Across Spain. The book details the father-son expedition along the 500-mile pilgrimage as they attempt to connect on a deeper level and have candid, honest conversations about their relationship, life, fame and more.

The trek is one McCarthy, who became a household name with coming-of-age 1980s films like Pretty in Pink, St. Elmo's Fire and Less Than Zero, is familiar with. The actor embarked on the same walk about three decades earlier when he was much, much younger and recalled having a "life-changing" experience. "I always wanted to do it again and then as Sam was cusping adulthood, I thought it might be a great thing for us to do together," McCarthy, 60, told ET's Rachel Smith in New York City in an exclusive sit-down with Sam, who most recently played Christina Applegate's TV son on Dead to Me.

"I was in a very different place in my life," McCarthy said of the first time he walked Spain when he was younger. "I was alone in the world. I had no kids and I had just [had] all that early fame with the Brat Pack stuff so I was also finding my own feet. It really helped me do that and I just thought it might be nice, as Sam was growing, to rewrite our relationship a bit -- not having it be so parent-child as opposed to two equal adults, to establish what that might be like. Sam, at one point in the journey, said, 'It's really hard to see your parents as real people,' and I think the inverse is true, so the journey was an effort to see each other for who we are."

Sam was 19 when he joined his father on the trip and he revealed he "was in a weird place in [his] personal life" following the end of Dead to Me. So when the possibility of joining his father on the trip came up, it seemed like time for a reset. "He had always talked to me about the walk and... I was like, yeah, I'll walk across Spain," the now-21-year-old shared.

There were highs and lows for the father-son duo as they walked the Camino together. At one point, Sam questioned what the point even was, McCarthy reveals in the book. (The Camino de Santiago is considered a UNESCO World Heritage site.) Eventually, Sam found meaning. "A grounding happens and a sense of accomplishment happens," he reflected.

Spending time together every day meant seeing "the good, bad and the ugly" and Sam confirmed his father is "incredibly impatient." "If he’s waiting in a line, he'll just have a panic attack. But on the inverse of that, he was incredibly patient with me," he credited. "He listened to me talk about whatever was on my mind for hours a day, would wait for me to get out of bed -- not that he didn’t put up with me before. But I suppose it showed a real -- I don't know if patience is even really the right word." McCarthy chimed in: "Love."

While the pair disagreed on how many fights they had along the way (Sam says "one or two," McCarthy seemed to imply more), McCarthy credited his son for being much "more easygoing" and able to "recover from friction much quicker" than he is. The trip afforded them the tools to approach conflict differently in their real life. Sam posited, "On my end, I could probably be more open with him. I think he’s probably still a little resistant to tell me if he’s really anxious about something. I tend to learn the most about him from reading his books."

Though the walk served as a backdrop for the pair, the book also touches on the early days of their relationship. In it, McCarthy shared why he revealed he was an actor to his children only about a decade ago. As he reflected upon the revelation, it's one of his life's regrets for not pulling them into his world sooner. "I had this inverse notion to protect my children. I guess I found it so traumatizing in a certain way when I was a young movie star, I found it so assaultive to my sensibility in a certain way," he explained. "I loved it and it was exciting and wondrous but it was also very frightening. So I think I tried to guard my children from all that stuff."

"I mention this in the book; we were in Wyoming... You were about eight or nine. A waitress came up and recognized me and wanted to take pictures," McCarthy said, recalling a memory with his son. "It was all very embarrassing and afterwards I said to Sam, 'Well, was that OK for you, Sam?' And he said, 'Oh, Dad, I was so proud.' At that instant I realized I'd done everything wrong by hiding this huge part of my life from my kids. Since then, it's all been on the table."

At the end of the book, McCarthy expresses immense gratitude for having the opportunity to accomplish the 500-mile walk with his son.

"I had the greatest gift you can have with an adult child, which is the luxury of time, and even as we were finishing it, I knew it would never come again in that way. Maybe we'd walk it again someday, but it would never be like that again, so I found that deeply moving -- even for the good times and not so great times," he recalled. "I was just grateful for that moment. One of the things about walking is it's a natural rhythm of processing things and when you really get back down to yourself and to who you are, gratitude is something that naturally rises off. It’s a beautiful life; it's great we're here."

Would Sam follow in his father's footsteps and do it all again? "I’ll definitely do it again," Sam answered. "I loved the Camino. The Camino was fantastic and when I said 'the 10/10 thing I’ve only done in my life,' I mean it." The younger McCarthy already has his sights set on potential next destinations -- Te Araroa, also known as The Long Pathway, in New Zealand and a rigorous 88-temple walk in Japan -- but seemed keen on returning to Spain to have another go.

Could his father join him for round three? "Give me a few more years, but not too many," McCarthy quipped, to which Sam said, "But I would do it again with him. Maybe... probably."

About two weeks ago, McCarthy posted on his Instagram that he had recently reunited with Rob Lowe, with whom he starred in 1983's Class and later St. Elmo's Fire, before not crossing paths for another 30 years, for an upcoming documentary on the Brat Pack he was working on.

"It seems crazy," McCarthy said when asked about their reunion, adding that he also reunited with another fellow Brat Pack-er, Emilio Estevez, for the doc. "I went back and started hunting everybody down again and we just hadn't seen seen each other in all these [decades]. So it was great to catch up with everybody again."

Walking With Sam: A Father, a Son and Five Hundred Miles Across Spain is out now.

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