You are still my ugly littler sister

Bonjour tout le monde. Voilà je viens de terminer la leçon shopping for mom 12 et je suis tombé sur cette phrase : you are still my ugly littler sister.( je suppose que c’est little et non littler)
En la traduisant je suis tombé sur la signification suivante : tu es toujours ma petite soeur vilaine.
Je suppose que c’est une expression, j’ai parcouru le net, mais je n’ai pas réussi à en trouver le sens.
Si quelqu’un pouvait m’aider, j’en serais très heureux.

Ugly = not pretty. Little, littler, littlest. This is an older brother teasing his little sister, that’s why he is using ‘ugly’ and ‘littler’.

There’s the Hans-Christian Andersen story of The Ugly Little Duckling who starts out by being different and ‘ugly’, but who turns out to be a beautiful swan. So, the teasing of ‘ugly’ is not quite as mean as it sounds…

Mon Dieu c’est super, je te remercie. Je n’avais pas compris le fait qu’il soit plus agé qu’elle ! Merci beaucoup pour l’histoire d’Andersen.

The term “littler sister” is unusual, and given the history of typos in that series of lessons, I would assume that the author meant to say “little sister” which is the common expression.

I listened to the lesson and Steve was right, it was a typo: I have changed it to ugly little sister.

Thank you Steve and SanneT.