A former chief executive of Save the Children faced three complaints of inappropriate behaviour towards female staff before leaving the charity, the BBC has learned.
Justin Forsyth was accused of sending inappropriate texts and commenting on what young female staff were wearing.
Mr Forsyth said he had "apologised unreservedly" to the three workers.
It comes as Oxfam and Save the Children have separately been quizzed by MPs about sexual misconduct by workers.
Although not accused of sexual misconduct, Mr Forsyth, who is now deputy executive director at Unicef., said he had had "unsuitable and thoughtless conversations" with staff.
He said the concerns were handled through a process of mediation and no formal complaints were made.
He added he thought the issue had been closed "many years ago".
Save the Children said it had commissioned "a root and branch review of the organisational culture" at the charity "addressing any behavioural challenges among senior leadership".
The charity said concerns were raised about "inappropriate behaviour and comments" by Mr Forsyth in 2015.
It said two trustees carried out separate investigations into a total of three complaints made by female employees.
"Both reviews resulted in unreserved apologies from the CEO. All the parties agreed to this and the former CEO apologised to the women in question. At that time the matters were closed."
A Unicef spokesman 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."
'Exposed to bravado'
An investigation by BBC Radio 4's PM programme, found the complaints against Mr Forsyth included women receiving a series of inappropriate texts, and comments on how they looked, what they were wearing and how he felt about them.
If they did not respond, Mr Forsyth would follow up his messages with an email, asking if they had seen the text.
If they still did not respond, he would ask someone to send them to him for a "quick word".
A woman who complained at the time said the longer she was at the charity the more she was exposed to "some of the bravado".
"That is both at head office and in the field," she said.
"Other women tell you to watch out for certain senior people. You start to hear rumours about some of the directors but of course until it happens to you - which it did - you don't really appreciate how hard it is to deal with."
She said it did not seem the complaints were being treated with the "appropriate degree of seriousness" and it was "troubling" that the then chairman of the charity's board of trustees, Sir Alan Parker, became involved.
Sir Alan is the founder of the PR firm Brunswick.
Another former employee of Save the Children told the BBC: "The centre of this crisis was not in Haiti or Chad. It was in London.
"Young professional women at Save the Children felt unsafe. They felt that their careers could depend on ensuring they responded to unwanted attention and to bullying."
In his statement, Mr Forsyth said he had 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 allegations come after Brendan Cox - the husband of murdered MP Jo Cox - quit two charities he set up in memory of his wife amid allegations of inappropriate behaviour.
The Charity Commission said it had "extensive regulatory engagement" with Save the Children after allegations of misconduct and inappropriate behaviour were made against Mr Cox and Mr Forsyth between 2015-16.
A spokeswoman added that the body received an independent review "commissioned by trustees", and "received direct confirmation and assurance from trustees" that recommendations made to the charity "were being urgently acted upon".