Tristan and Khloe's son, whom was birthed via surrogate, marked his first birthday on July 28.
On Saturday, the proud dad dedicated a message to his baby boy -- who celebrated his first birthday on Friday.
"Tatum!! Happy birthday my son! You are a reminder of what life represents to me. You have taught me every loss comes a lesson and you are my gift. You are my reminder of all of God’s messages. You are the reason that I began my story. The mistakes along the way are lessons not failures. There is no expiration date to reinventing yourself. Tatum your sweet soul reminds me of God’s grace. You are a future king my son and I am so blessed to be your DaDa!," he wrote.
Tristan began his post with a picture of him holding Tatum as they both smile while wearing matching sunglasses. In the follow-up pic, the Los Angeles Lakers player's baby boy smiles while looking at him.
The NBA star is also the father of True, 5, whom he shares with Khloe. Prince, 6, whom he shares with ex-girlfriend Jordan Craig, and 1-year-old Theo, whom he shares with Marlee Nichols.
Khloe, 39, and Tristan, 32, welcomed their son via surrogate after they ended their relationship in 2022.
Tatum's big social media debut began on Friday when Khloe and her family shared rare pictures of her baby boy in honor of his special day.
"Happy birthday, my sweet son! I am a firm believer in that God gives you what you need and I needed you. God knew my heart needed you. I needed your sweet and precious Smile. I needed your angelic spirit. I needed a love only you could give me. I needed my son," the Good American founder wrote.
"I am so proud to be your mommy. So proud of the love and laughter we have in our house. So proud of your beautiful, gentle, loving, infectious spirit. You light up every single room. There’s no denying that Everyone smiles when they look at you! Especially True she is so proud to call you hers. Tatum, You have changed mine and True’s lives forever. We both needed you."
She continued, "I knew she would be a fantastic, loving older sister, but I don’t think I ever could’ve imagined the love and bond you guys already have. You both remind me so much of uncle Bob and I. It’s fitting since I think you look soooo much like your uncle. (Which means I think you look like my dad too) I cannot believe you are already one happy first birthday my sweet sweet baby."
Khloe ended her message dedicated to her "little Armenian man" with a verse of "You Are My Sunshine."
Kris Jenner and Kim Kardashian also got in on the love, sharing birthday messages in honor of Tatum's first birthday.
Khloe has been candid in the past about her struggle with welcoming Tatum via surrogate in July 2022. She previously alleged that Tristan "encouraged" her to do an embryo transfer just days before news broke that he had fathered a child with Maralee Nichols while engaged to Khloe.
The pair subsequently split and Khloe struggled to keep the news she was expecting a second child quiet. On season 3 of The Kardashians, Khloe also opened up about feeling "less connected" to Tatum due to the surrogacy process and the drama surrounding her and Tristan.
"I definitely was in a state of shock from my entire experience in general," she said of her time in the hospital welcoming her son. "I felt really guilty that this woman just had my baby and then I take the baby and I go to another room and you're just sort of separated. I felt it's such a transactional experience... I wish someone was honest about surrogacy and the difference of it. But it doesn't mean it's bad or good. It's just different."
In the season 3 finale of the Hulu series, Khloe shared that it has become "easier" for her to connect with Tatum as the months have gone on.