Founder member Mutya Buena has left pop trio Sugababes, saying she felt unable to commit to the act for another year.
Buena (centre) has been in the pop act since she was 13 years old
The 20-year-old was in Sugababes for seven years, as they scored four number one hit singles in the UK.
Buena, who gave birth to first child Tahila in March, will be replaced by a new member to be revealed in 24 hours.
"I felt that the commitment I would need to make to Sugababes over the next 12 months was something that would become compromised by me," she said.
Buena was in the original Sugababes line-up with Keisha Buchanan and Siobhan Donaghy, who had their first hit single Overload in 2000.
Donaghy left the group one year later during a Japanese tour, to be replaced by current member Heidi Range, 22.
The trio went on to have a further three hit albums and number one singles Freak Like Me, Round Round, Hole in the Head and Push the Button - a chart-topper for three weeks in October.
They were named best British dance act at the Brit Awards in 2003 and Freak Like Me was best single at the 2002 Q Awards.
Sugababes are due to tour in March and April and to support Take That on their reunion tour next summer, dates which they said they would honour with an unnamed new singer replacing Buena.
In a statement released on the act's website, Buena said on Wednesday that her decision to quit was "based purely on my personal reasons".
"It was very difficult but definitely not a snap decision," she added.
"There comes a time when everyone wants to re-evaluate their life and what they want out of it."
Buena added that her departure "would never mean the end of Sugababes".
Buchanan said: "It goes without saying that we will all miss Mutya, but we also knew there was still a place for bringing in somebody new who could help us carry on taking the Sugababes brand of music forward."
Range said the act's unnamed new member - chosen by the band's management team - had "an amazing voice" and "looked great".
"When we all met her, we instantly knew she was the only person to share the rest of the journey with us," said Range.