Tristan Thompson's Son Theo Turns 6 Months Old -- See Mom Maralee Nichols' Sweet Tribute

The proud mom gushed over her baby boy!

Maralee Nichols is celebrating half a year with her baby boy! The mother of Tristan Thompson's son took to Instagram on Wednesday to mark their baby, Theo's, six-month birthday.

Nichols shared a shot of herself and Theo, which was taken from behind, enjoying a day at the zoo.

"Can’t believe my baby is 6 months old," she marveled in the caption. "Theo’s first time at the zoo, he loved looking at all the animals."

Nichols' post came the month after she celebrated her first Mother's Day. The mother-son pair posed for a photo shoot for the occasion, with Nichols wearing a flowing, off-white dress as she held her son, who wore a grey ensemble.

At the time, Nichols' rep told ET that the adoring mom and her son were "spending a quiet day together with loved ones" to celebrate the holiday.

"Words cannot express how much I love you, being your mommy is my greatest blessing," she wrote on Instagram in May. "You are my world. Happy Mother’s Day to all of the amazing mothers out there!"

In January, following a prolonged legal battle, a paternity test confirmed that Thompson is Theo's dad. The NBA star fathered Theo during a brief reconciliation with Khloe Kardashian, with whom he shares a 4-year-old daughter, True. He's also dad to Prince, 5. He shares his oldest tot with Jordan Craig.

The month after her baby's paternity was confirmed, Nichols revealed the newborn's name in a statement to ET.

"Theo, my little angel baby. I named you Theo because it means, 'Gift from God.' I had never been pregnant and had been told I might not be able to have children. I couldn’t believe I was pregnant, when I saw you on the ultrasound and heard your little heartbeat, I knew I would always protect you and keep you safe," she said. "I love you more than you’ll ever know. You bring such joy and happiness into my life. My greatest blessing."