Khloé Kardashian and Tristan Thompson have officially change their son Tatum's last name. According to documents from US Weekly, the former couple son's last name is now legally Thompson. Originally their son's full name was Tatum Kardashian when he was born last year.

Tatum Thompson is now 13 months old and the Khloé admitted that finding a name for him was not easy.

“At first, I really did not know what I was going to name him,” she said when she appeared on The Jennifer Hudson Show back in April. “I wanted to meet him and feel him out a little bit. And so, at first, he didn’t have a name. Then, he’s been named, but I’ve been waiting for the premiere of our show and I didn’t know it was going to be this far out, so now, if my daughter outs me, I’m screwed.”

The former couple also share a five-year-old daughter, True Thompson who just started kindergarten this week.

“For anyone wondering, no I’m not ok!” Khloe wrote on Instagram alongside a photo of True. “Next it will be prom.”

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True is now a big sister and just like all of the Kardashian/Jenner children, Tatum also had a large birthday party last month which was space-themed. Khloe penned a heartfelt message on Instagram for her youngest child who turned one.

“I am a firm believer in that God gives you what you need and I needed you. God knew my heart needed you,” Kardashian wrote via her Instagram last month hours before the party. “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.”

She added: “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.”

While True and Tatum are Khloé Kardashian's only children, Tristan Thompson is also the father to son Prince Oliver, 6, with Jordan Craig, and Theo, 20 months, with Maralee Nichols.