The public service broadcaster engaged in a "significant breach" of broadcasting rules by not revealing that the voice of a programme about the Gaza conflict was the offspring of a Hamas representative, according to British broadcasting authority Ofcom.
An probe by the media regulator into Gaza: How to Survive a Warzone has determined that the programme was "substantially inaccurate".
The head of the BBC had already issued an apology, saying there had been "a serious error in relation to truthfulness".
Ofcom has ordered the BBC to air a prime-time declaration about its conclusions.
"As this represents a serious breach of our code, we are ordering the broadcaster to air a message of our findings against it on BBC2 at 9pm, with a date to be determined," it said.
'Potential to Damage Trust'
The authority's report declared: "Our investigation determined that the film's lack of disclosure that the narrator's parent occupied a role in the Hamas-controlled administration was materially misleading.
"Consequently that the audience did not have critical information which may have been extremely pertinent to their assessment of the voice and the content he provided.
"Trust is at the heart of the connection between a broadcaster and its audience, notably for a state-funded media outlet such as the British Broadcasting Corporation.
"This failing had the potential to damage the significantly high levels of credibility that the public would have invested in a documentary produced by the BBC about the conflict in Gaza."
The documentary was removed from the BBC's streaming service in last February after the presenter's familial connections emerged, and in this past July an corporation's own inquiry concluded it breached the corporation's editorial guidelines on factual correctness.
A corporation official said: "The regulator's decision is in accordance with the results of the internal assessment, that there was a significant failing in the film in relation to the corporation's content standards on factual correctness, which reflects regulation 2.2 of the regulator's media standards.
"We issued an apology for this and we agree with the authority's determination in full. We will comply with the sanction as soon as the timing and language are finalised."
