S15E20 The Way We Weren't
Homer tells the children of his first love at school,a girl who actually turned out to be Marge but whom he failed to recognize because she had burnt her blue hair brown ironing it. Marge takes up the story,explaining that they were to meet for a second date but Homer failed to show. Homer explains it was because he accidentally ended up in Fat Camp and could not escape in time. However each has kept the half of the heart-shaped love token they exchanged as proof of that first meeting.