The phrase "ugly sister" is used to refer to someone who is less attractive or less popular compared to someone they are associated with, often a sibling. Full definition
While people have mixed feelings about this alleged «waste of real estate» and «ugly sister of bezels», the notch does serve two purposes. (themrphone.com)
The core cities were ugly sisters at the Treasury ball, arriving after Cinderella Bernstein had already captured Prince Osborne's heart. (theguardian.com)