Save the Children are to be investigated over its response to misconduct and harassment claims against senior members of staff.
The probe by the Charity Commission will consider the response to claims such as those made against the charity's former chief executive Justin Forsyth and Brendan Cox, husband of the murdered Labour MP, Jo Cox.
The Charity Commission will open a statutory inquiry into how allegations of misconduct in 2012 and 2015 were dealt with and whether they were fully disclosed to the regulator.
Earlier this year, it emerged that between April 2016 and March 2017, Save the Children had 31 allegations of sexual misconduct - 10 of which were referred to the police.
A leaked 2015 report from the charity suggested that its chairman Sir Alan Parker's "very close" relationship with Mr Forsyth, who left the charity in 2016, may have affected how he responded to complaints.
In 2015, Mr Forsyth apologised unreservedly to the three women who had made the allegations. He quit his role as deputy executive director of Unicef when the allegations resurfaced in February this year.
Meanwhile, Mr Cox, who was Save the Children's chief strategist in 2015, admitted that he made "mistakes" and behaved in a way that caused some women "hurt and offence" when he was working at Save the Children.
Mr Cox resigned from the charity in September 2015, amid the allegations of inappropriate behaviour towards women, but at the time denied that was the reason he quit.
Michelle Russell, director of investigations and enforcement at the Charity Commission said: "Opening a formal investigation does not necessarily mean that we have concluded that there has been wrongdoing by the trustees of The Save the Children Fund. However, we do have questions that must be answered, and we need to hold the charity formally accountable for providing them in a clear and timely manner."
Peter Bennett-Jones, the chair of Save the Children UK’s Board of Trustees, said: “It is critical that Save the Children works with the Charity Commission to examine whether mistakes were made in the past. If mistakes were made they will be fully acknowledged and properly addressed.
"We are committed to working with the Charity Commission to establish a truthful and accurate account of events and the charity’s response. If mistakes were made, we will act swiftly and decisively to address them."
The commission said it will publish a report once it has concluded the inquiry.