It was an unfortunate thing that of the three of them, Gumball was neither human nor human-based. Unlike Marshall Lee the Vampire King, still in possession of his human half despite vampirism, and Fionna of the Grasslands, pure-bred human, the High Esteemed Prince Gumball was merely humanoid. This afforded him nothing when it came time to talk the dreaded subject of parentage; because, ostensibly, the threefold lovebirds wanted a little tyke to call their own.
Fionna gave him a knowing look, and a kiss, and Marshall stared him dead in the eye and apologized heartfelt for the first time in a millennium. Gumball shook it off, because he knew it far before they would, his mind a million paces ahead of any other that existed, had existed, and wouldexist forever, he knew that as much as the kid would biologically be Marshall's and be Fionna's, the child would also be his in other manners, and he would be the father to it as much as Marshall would be.
The threefold lovebirds had a habit of sharing, and the love and trials of parenthood was one of those things.
Notes: I had a little plot bunny crawl from under the couch. He also brought some friends, but before I write anything else, I want to give the other half of the perspective of this situation. It'll be up soonish I figure?