Billie Marten: Having SAD made me write the happiest pop song

Billie Marten's Blue Sea, Red Sea featured as Annie Mac's hottest record on Radio 1 recently.

This came just a year after the 19-year-old was diagnosed with severe seasonal affective disorder (SAD).

It's a type of depression caused by changes in the seasons, particularly in the winter, and is estimated to affect one in 15 people in the UK.

The condition has inspired Billie's latest single and here she explains the meaning behind the lyrics.

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