Amelia Fieldmouse, currently known as Felicity Fieldmouse or simply Mrs. Fieldmouse, is an anthropomorphic mouse who is Mickey Mouse's sister and Morty and Ferdie's mother.
As of yet, she has not made any appearances in animation.
She first appeared in Morty and Ferdie's 1932 debut strip, Mickey's Nephews, as a mouse lady arriving at Mickey’s house and drops the twins off, asking if Mickey would not mind caring for them while she's running an errand. In the Dutch comic strips, Mickey referred to her as “Amalia” (Dutch spelling for the name "Amelia"), while in the English version she is referred to as “Mrs. Fieldmouse. The original strips do not make clear that Amelia is Mickey's sister; as drawn, she looks more like an elderly relative. However, the relationship was clarified when she reappeared in more recent comics. The fact that Mickey is Morty and Ferdie's maternal uncle was also made clear by the fact that, in the 1935 one-pager He's a Knockout, Mickey states that he hasn't got a brother.
At Egmont Publishing, Amelia was given her current name Felicity Fieldmouse. As a side note, Egmont also named Felicity's husband—the twins' father—Frank, though he has yet to be specifically named or depicted in a published comic. Egmont's modern version of Amelia has slimmed down and is designed to look closer to Mickey in age, while remaining significantly taller than him.