ugly duckling
US /ˈʌɡ.li ˈdʌk.lɪŋ/
UK /ˈʌɡ.li ˈdʌk.lɪŋ/
1.
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.
•
The old building was considered an ugly duckling, but after renovation, it became the most beautiful one in the city.