Three people involved in allegations of "sexual misconduct incidents" resigned or were dismissed from a multimillion-pound disaster aid charity.
Shelterbox only made a report to the Charity Commission when the BBC asked a series of questions.
The Charity Commission said: "We are assessing these serious concerns as a matter of urgency."
The revelation comes in the wake of a series of allegations of sexual misconduct by aid workers.
The charity told the BBC there had been "three sexual misconduct incidents pre-2013, one of which is unproven".
The Charity Commission said a serious incident report was submitted on 8 March concerning "non-recent" incidents.
The BBC had contacted Shelterbox on 6 March with a series of questions relating to allegations of staff paying for sex, and any complaints made and action taken.
The charity has not explained why it did not previously report the serious allegations and said they were "still under investigation".
The Charity Commission said it was in touch with Shelterbox to understand whether the alleged incidents "were handled appropriately at the time".
Shelterbox was set up in 2000 in Helston, Cornwall, by former Royal Navy search and rescue diver Tom Henderson.
Originally the charity delivered green boxes containing essential items, such as a stove and a tent, for people in disaster areas .
In 2014 Shelterbox started providing shelter kits which contain "all of the essential tools people need to start repairing and rebuilding homes".
The charity has delivered aid at the scene of disasters areas, including Typhoon Haiyan in the Philippines, flooding crises in Malaysia and the aftermath of Hurricane Matthew in Haiti.
Chris Warham, Shelterbox chief executive, said: "These incidents did not involve beneficiaries, were managed swiftly and effectively at the time through immediate dismissal and resignation but were not reported to the Charity Commission, which we should have done."
The exact nature of any incidents and when and where they took place is still not known.
Shelterbox has an annual income of more than £10m and its president is the Duchess of Cornwall.
In 2012, the charity's chief executive and founder Tom Henderson was sacked and later charged with fraud but found not guilty in court.
Shelterbox has told the BBC that Mr Henderson was not involved in any way with the alleged sexual misconduct.
Mr Henderson said he was not aware of the allegations.
Trustees of any charity are obliged to report any serious incident to the Charity Commission "in a timely manner".
The Charity Commission guidance on safeguarding states: "If you fail to report a serious incident that subsequently comes to light, the Commission may consider this to be mismanagement..."
A spokesman for the Duchess of Cornwall declined to comment.
According to Shelterbox, the charity had an income of £108m between 2000 and 2015 with more than £43m coming from Rotary International.
A spokesman for Rotary International said: "Rotary has, until very recently, been unaware of the historic safeguarding issues that Shelterbox has now disclosed to the Charity Commission, and it would be inappropriate to comment further until the Commission concludes its review."