Thread:Normalhuman/@comment-14250-20171028204537/@comment-31558698-20171028205825

In "The Signature", Karen, while signing Jojo and Louie's marriage paperwork, she says:
 * "Congratulations, Mr. and Mrs. Watterson."

Thus implies that Louie has legally taken Watterson as his surname, making his name Louie Watterson.