Gwyneth Paltrow was a secret early source for journalists investigating Harvey Weinstein, and played a "much more active" role than previously known in the events that ultimately led to his arrest.
The actor was one of the first people to pass information about the movie mogul to New York Times journalists Jodi Kantor and Megan Twohey, they have revealed.
On one occasion, Paltrow faced a "hair-raising" situation as Weinstein turned up early at her house for a party she was hosting, unaware that she was already speaking to journalists about him.
Paltrow hid in her bathroom and rang the journalists, saying: "What do I do? He's here!"
Her role is detailed in Kantor and Twohey's book She Said, which details events leading to Weinstein's arrest, and the MeToo movement. The journalists first started writing newspaper articles about sex allegations against Weinstein in October 2017.
Kantor said: "She [Paltrow] did play a much more active role than anybody's ever known. But it was hair-raising for her, because Harvey Weinstein had been such an important influence."
Paltrow won an Oscar for best actress in 1999 after working with Weinstein on Shakespeare in Love.
Twohey said: "Gwyneth Paltrow was one of Harvey's biggest stars, and he had really presented himself as a godfather to her ... So, I think many people will be surprised to discover that, when so many other actresses were reluctant to get on the phone, and scared to tell the truth of what they had experienced at his hands, Gwyneth was actually one of the first people to get on the phone."
Paltrow had, from an early stage, been "determined" to help the investigation, "even when he [Weinstein] turned up early to a party at her house, and she was forced to hide in the bathroom".
Twohey added: "Harvey Weinstein was [scared], what the implications would be if his biggest star actually ended up going on the record."
Early in their investigation, Paltrow told them she had gone to a meeting with Weinstein in a hotel room when in her early 20s. She claimed he put his hands on her, saying: "Let's finish in the bedroom".
As allegations unfolded against Weinstein, Paltrow agreed to make her story public.
Kantor said: "There are so many good reasons not to go on the record with a story like this.
"The famous women often felt 'this will become a sleazy Hollywood sex story that I don't want to be part of'."
Weinstein denies charges of rape and predatory sexual assault.