Gwen Stefani Snapchats Son Apollo's Adorable 3rd Birthday Celebration at School -- Watch!

Happy birthday, Apollo!

Gwen Stefani's little boy turned 3 years old on Tuesday, and she couldn't help but document his adorable school celebration on Snapchat.

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Stefani's youngest son with ex Gavin Rossdale enjoyed some toothbrush painting with friends, a little music class, and finally a delicious chocolate cupcake, before he and his classmates went after a Captain America piñata.

WATCH: Gwen Stefani's Son Apollo Shows Off His Rock Star Skills, Sings With His Mom in Adorable Snapchats

ET sat down with Rossdale earlier this month, where he opened up about his and Stefani's plans for Apollo's dinosaur-themed birthday party.

"Isn't that weird? Anthropology. Little boys just want dinosaurs! Where do you get that from?" Rossdale mused. "I'm sure he saw a book in his brother's room, but he's crazy for dinosaurs, so we have a party for him and a lot of dinosaurs involved."

"I'm going to have a smaller [party] for him," he revealed, adding that he and Stefani are able to co-parent because of their shared interest in their boys.

"We both have the same interest at heart, their happiness," he said. "It's really simple."

WATCH: Gavin Rossdale Gets Candid About Ex-Wife Gwen Stefani: 'I Still Think Gwen Is Incredible'

See more from ET's interview with Rossdale in the video below.