Save the Children has apologised to women employees who complained of inappropriate behaviour by the charity's former chief executive, admitting their claims were not properly dealt with at the time.
In a statement, the charity said Justin Forsyth - who has since gone on to become deputy executive director of Unicef in New York - was twice subject to investigation after concerns were raised about his conduct in 2011 and again in 2015 involving in all three women.
The disclosure comes after Brendan Cox, the widower of murdered MP Jo Cox, 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 and Mr Forsyth had previously worked together at 10 Downing Street under Gordon Brown.
Mr Forsyth has admitted making "some personal mistakes" during his time at Save the Children.
On each occasion - following an inquiry carried out in conjunction with an independent trustee - Mr Forsyth issued an "unreserved apology" to the women concerned and the matter was considered to be closed.
However the charity said that concerns were subsequently raised with the trustees that "matters should not have been left as they were" and a further review was required.
That review found that human resources process "had not been followed in every aspect", the statement said.
Mr Forsyth said in a statement: "I made some personal mistakes during my time at Save the Children.
"I recognise that on a few occasions I had unsuitable and thoughtless conversations with colleagues, which I now know caused offence and hurt.
"When this was brought to my attention on two separate occasions, I apologised unreservedly to the three colleagues involved.
"My apologies were accepted and I had thought the issue closed many years ago.
"The concerns were handled through a process of mediation and no formal complaint was made.
"I also want to make clear I played no role whatsoever in the disciplinary proceedings against Mr Cox nor their outcome.
"I was rightly recused from the case from the outset.
"This was handled professionally by an independent legal firm with the board and HR."
Unicef said it was aware of the past complaints against to Mr Forsyth.
A spokeswoman said: "We welcome Mr Forsyth's decision to come forward and acknowledge past mistakes.
"We are discussing this matter with Mr Forsyth and his former employer so we can take appropriate action."
On Sunday, Save the Children's current chief executive Kevin Watkins announced a "root and branch review" of the charity's "organisational culture", including measures to preserve staff safety and "any behavioural challenges among senior leadership".
A Save the Children spokesman said: "We apologise for any pain these matters have caused and sincerely hope that the complainants feel able to help us with the review in the coming weeks.
"This is so that we can better support our skilled and highly valued staff as they help change the lives of millions of children around the world every day."