Billie Eilish looks fresh-faced after a workout in Los Angeles

Billie Eilish looked fresh-faced and upbeat after causing outrage from many fans for her age-gap Halloween costume with older boyfriend Jesse Rutherford.

The 20-year-old pop star was spotted chatting with a friend after leaving a workout session in Los Angeles on Wednesday.

The outing came just days after she made her relationship with Jesse Rutherford 'Instagram official,' though her baby costume and her 31-year-old boyfriend's old man costume - poking fun at their age gap - was no laughing matter for many fans.

The Lovely hitmaker was spotted out wearing a black short-sleeved t-shirt with short black bicycle shorts for her workout.

The singer completed her look with a pair of black sneakers and black socks for her mid-week workout.

Eilish used the weekend's Halloween festivities as an opportunity to go 'Instagram public' with her boyfriend Jesse Rutherford.

She shared a number of photos and videos from her Halloween weekend on Tuesday, the last of which was her dressed as a baby and her singer-songwriter boyfriend dressed as an old man.

The photo was widely circulated on social media, with many fans expressing their frustration and disgust with the couple poking fun at their 11-year age gap.