sidechick

the other woman; also known as a blond mistress with blue eyes, a female that is either a male‘s wife or girlfriend who has relations with the male while he is in another relationship.

Andja: Look at Tijana and 👨🏻 🦱 are they going out?
Sara: No Andja! 👨🏻 🦱 is dating 👩🏻

Tijana is just his sidechick.