"Wow, I can't believe it's already been a year since this beautiful bald man that I can proudly call my dad passed away," Nathen wrote in a touching tribute to the late Sex and the City star on Instagram, Wednesday.
His words came alongside a series of throwback photos of Nathen, 21, and Willie throughout the years.
In his caption, Nathen recalled the things he missed about his dad. "Besides his head, I think I miss his laugh and smile the most. Because I knew that whenever he was laughing he wasn't the only one laughing," recalled Nathen.
He went on to praise Willie's ability to entertain, saying, "He had a gift of being able to talk to literally anyone he came into contact with and make them either laugh or awkwardly smile from a joke he had probably just told them."
Willie adopted Nathen in 2009 when he was only 7 years old, when meant Nathen had many years of experiencing the actor's sense of humor at play.
"I had heard the same 3 or 4 dad jokes from the time I moved in at 7 to when I turned 15. So at least a hundred times each joke and I would beg him to get a new joke," said Nathen. "Now, however, I wouldn't be upset to hear him say those same jokes a thousand or even a million more times."
But mostly, Nathen cherishes the lessons he learned from his dad.
"He wasn't just my father, he was my best friend and a mentor before I even knew what that was," said Nathen. "He inspired me when I was younger to be better than I ever thought I could and because of that I try to always do better."
"I would not be where I am today if not for him," Nathen added, "I wouldn't be who I am if not for him."
Said Nathen, of his dad: "He taught me to care about others and showed me how to love when all I had ever know was to fight for myself and care only about myself. He was always making people smile and laugh even when he was upset or furious and watching him do that as I grew up made me want to do that..."
Tommaso Boddi/Getty Willie Garson and Nathen in 2019
Willie, best known for his role as Stanford Blatch in Sex and the City and its revival And Just Like That..., died from pancreatic cancer last September at the age of 57.
In the caption, Nathen also admitted in the caption to being "selfish again" and "not the person he'd raised me to be" after his death.
"It's important to revisit the past, but it's also just as easy to get stuck in the past," he wrote. "It's more important to remember that there's also a tomorrow and a future."
He continued, "As you move forward, make sure you smile and live life to its fullest…because no matter how much time you might think you have, I promise you there's less. Life comes and goes way too quick so cherish everyone and say hi to a stranger every once in a while because you never know when you could meet your next best friend. That's how my dad met me."
"Thank you for all the lessons dad ❤️," Nathen ended the caption.
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In the comment section, friends of the late actor poured in love and support for the grieving son.
"I love you Nathen," wrote Hilarie Burton — who following Willie's death, got a tattoo in memory of the actor. "Your dad was exceptionally good at making others feel seen and special and loved. He was so so good to me. I love him and I'm grateful he gave you to all the rest of us."
The One Tree Hill star continued, "You Garson boys have a big chunk of my heart. Come to NY. Xoxoxo."
"Oh Nathen sending you all of our love!" wrote fellow Sex and the City star Kristin Davis. "We are all going to be together today and i feel him here with us. Thinking of all of the jokes he made the last time we did all of these things together. Thank you for this ❤️❤️❤️❤️❤️❤️❤️"
Tiffani Thiessen also sent Nathen some love in the comments. "He is so missed Nathen," she wrote. "I miss laughing with him, where we could go stuff our faces together, what bottle of wine to drink and most of all, talking about how proud he was of you and all you continue to accomplish. Sending you so much love my dear. ❤️"
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"Brilliant Willie," he wrote to accompany one of the final scenes Garson filmed for SATC's revival And Just Like That.... "Missing you today and everyday my sweet hilarious friend.