Jesy Nelson has left Little Mix, saying being part of the pop group had “taken a toll on my mental health”.
She explained: “I find the constant pressure of being in a girl group and living up to expectations very hard.”
Writing on Instagram, the 29-year-old said being in the band had been “the most incredible time” but it was now time to “embark on a new chapter”.
Her former bandmates said it was “an incredibly sad time for all of us but we are fully supportive of Jesy”.
The news comes a month after Nelson said she was taking an “extended” break from the pop group for “private medical reasons”.
Leigh-Anne Pinnock, Perrie Edwards, and Jade Thirlwall performed as a trio on Strictly Come Dancing at the weekend.
In her statement, Nelson said she had made her decision “after much consideration and with a heavy heart”.
“I need to spend some time with the people I love, doing things that make me happy,” the singer continued.
The remaining members added: “We know that Jesy leaving the group is going to be really upsetting news for our fans.
“We love her very much and agree that it is so important that she does what is right for her mental health and well-being.”
They said they were “still very much enjoying our Little Mix journey” and would continue as a trio.
Little Mix formed on The X Factor in 2011 and has gone on to record six UK top 10 albums and four number-one singles. They are currently number five in the chart with their hit Sweet Melody.
Last year, Nelson was widely praised for discussing her mental health struggles in a BBC Three documentary.
The group was recently seen looking for a new backing band to join them on tour in the BBC One talent show Little Mix: The Search.