Here's to 13th Anniversary of Uncle Grandpa for a Day! #UncleGrandpa #13thAnniversary

Here’s to 13th Anniversary of Uncle Grandpa Ate My Homework! 🌈🎉 #unclegrandpa #13thanniversary

Here’s to 13th Anniversary of Uncle Grandpa Ate My Homework! 🌈🎉 #unclegrandpa #13thanniversary

Uncle Grandpa is about to put on a lightbulb.💡🌈 #ChangeALightDay #UncleGrandpa

Here’s to 12th Anniversary of Average Jeff, Aunt Grandma and Grounded! 💜🎉🌈💚 #unclegrandpa #clarence #12thanniversary #cartoonnetwork

Here's to 13th Anniversary of Uncle Grandpa Sitter! #UncleGrandpa #13thAnniversary

Here's to 12th Anniversary of The Password and Vacation! #TheAmazingWorldOfGumball #UncleGrandpa #TAWOG #Gumball #12thAnniversary

(UPDATE)

Other close calls (technically the last one had a pilot movie released in 2012, but the series itself was in 2013):

#WanderOverYonder #MickeyMouse #MickeyMouse2013 #UncleGrandpa #SofiaTheFirst

What is your most favorite TV cartoon from when you were 19 years old? Reply or Quote.

Here's to 13th Anniversary of Driver's Test! #UncleGrandpa #13thAnniversary

Here's to 12th Anniversary of Sick Bag and The Mothers! #UncleGrandpa #TheAmazingWorldOfGumball #12thAnniversary #CartoonNetwork #Gumball

#UncleGrandpa #BusoRenkin #VictorPowered #VictorGoodMorningAndWhoAreYouQuote

This old Clipchamp video of Victor Powered's hair onto Uncle Grandpa like it's a wig.

I Ms painted Victor Powered out that only his hair shows so I can Clipchamp edit his hair onto Uncle Grandpa.

Here's to 13th Anniversary of Moustache Cream and Nickname! #UncleGrandpa #13thAnniversary

Beary Nice and Hot dog Person from Uncle Grandpa (redraw from a 2020 doodle).
#unclegrandpa #cartoonnetwork

A very late but Here’s to Frankenstein! #UncleGrandpa #FrankensteinDay

Here’s to the 13th belated Anniversary of Space Emperor and Funny Face! 😃🎉🌈 #UncleGrandpa #13thAnniversary

Here's to 12th Anniversary of The Allergy and The History of Wrestling!

#Gumball #UncleGrandpa #TheAmazingWorldOfGumball #12thAnniversary

Here’s to Pizza Steve! 🍕 #unclegrandpa #nationalcheesepizzaday