Billie Eilish secretly had red hair for a week.

The 20-year-old popstar famously switched up her black-and-green hairdo for platinum blonde locks last year before going brunette and the end of 2021 and has now revealed she dyed her hair red during the transition period.

Alongside an Instagram post marked with the date November 22, she wrote : "I took the blonde out and went red for a week hehe" (sic)

The 'bad guy' hitmaker shared a photo of herself in the process of dyeing hair whilst wearing a black salon gown, sporting her flaming red locks.

Billie's latest hair transformation comes after last year's switch from black to blonde, which marked the beginning of her 'Happier than Ever' album era.

At the time, the singer had to conceal the lengthy process from her millions of fans and Instagram followers by wearing a wig that matched the dark mullet she had become known for, concealing the dye job for six weeks.

At the time, she told how she obtained the wig by ordering a costume from Amazon that was based on herself.

Speaking on 'The Late Show with Stephen Colbert', she said: "I knew that it would have these processing periods where it would look insane, and I didn’t want to look insane. But I needed something quick, so I literally ordered a Billie Eilish Halloween costume wig on Amazon."

However, the Grammy Award winner also admitted that her signature neon green look meant she "couldn't go anywhere" and she craved anonymity.

She told Elle: "I couldn’t go anywhere with that hair because it was so obviously me. I wanted anonymity."