ugly duckling

US /ˈʌɡ.li ˈdʌk.lɪŋ/
UK /ˈʌɡ.li ˈdʌk.lɪŋ/
"ugly duckling" picture
1.

vilain petit canard

a person or thing that is initially unattractive or unpromising but eventually becomes beautiful or successful

:
She was an ugly duckling in high school, but she grew up to be a stunning model.
Elle était un vilain petit canard au lycée, mais elle est devenue un mannequin époustouflant.
The old building was considered an ugly duckling, but after renovation, it became the most beautiful one in the city.
L'ancien bâtiment était considéré comme un vilain petit canard, mais après rénovation, il est devenu le plus beau de la ville.