Tristan Thompson Celebrates Son Prince Starting School: 'My Young King's First Day'

Tristan Thompson/Instagram

Tristan Thompson is celebrating a special milestone in his oldest child's life.

The NBA star shared a photo on Instagram in which he poses with 5½-year-old son Prince Oliver for his first day of school on Tuesday

"My young King's first day👑✏️📚," he captioned the sweet father-son shot.

Thompson wore a Supreme t-shirt and black pants with printed Nike sneakers for the occasion, while Prince wore a Moschino t-shirt and a pair of army green shorts, By his feet was a Grogu-print backpack with his name on the front.

Thompson shares Prince with his ex-girlfriend, model Jordan Craig. He also shares an infant son and daughter True, 4, with ex Khloé Kardashian and son Theo, 9 months, with Maralee Nichols.

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Last month, the NBA pro, 31, took to the court with Prince, sharing a photo of the future All-Star wearing his dad's Chicago Bulls jersey while he showed off his athletic prowess.

"Training Day," Thompson wrote on his Instagram Story.

"Starting them early," the proud dad captioned a follow-up clip of his son practicing his dribbling.

RELATED: Khloé Kardashian and Tristan Thompson Welcome Their Second Baby via Surrogate

tristan thompson/instagram

Though he has yet to comment on his now 5-week-old son with Kardashian, a source told PEOPLE last month that The Kardashians star, 38, wanted to maintain the co-parenting relationship.

"Just like they do with True, Khloé will co-parent the baby with Tristan," the source said at the time. "Tristan is the dad and Khloé wants him involved as much as possible. He is great with True."

A source previously told PEOPLE, "Khloé and Tristan are not back together."