"She said in the night she had been awakened by men knocking at her door that said they had been sent to her by Charles Taylor, and they had given her a very huge diamond," Farrow told the court.
Farrow said Campbell had then said she intended to give the diamond to the Nelson Mandela Children's Fund.
Fomer agent's testimony
Carole White, Campbell's former modelling agent who also attended the breakfast, also gave evidence on Monday that contradicted the model's version of events.
White said Campbell and Taylor, seated near each other at the dinner, had flirted during the meal.
At one point, "she [Campbell] told me he is going to give me some diamonds," White said. "She was very excited."
Taylor, meanwhile, "was agreeing there was something, a gift coming of diamonds".
"He was smiling and nodding in agreement," White said.
The former agent said that she had also been present when the diamonds were brought to Campbell's hotel room by two men.
"They took out a quite scruffy paper and handed it to Ms Campbell and said: 'These are the diamonds'," White testified.
"She [Campbell] showed it to me. She was quite disappointed because they were not shiny."
Campbell testified last week that she had received "dirty-looking stones" after the dinner.
But she told the court that she did not know who the gift was from.
Prosecutors had called the model to testify in the hope that she could provide evidence that Taylor had handled diamonds allegedly used to purchase weapons during the 1991-2001 Sierra Leone civil war.
Taylor is on trial on charges of murder, rape, mutilation, sexual slavery and conscription of child soldiers during wars in Liberia and Sierra Leone, in which more than 250,000 people were killed.
Campbell said at the trial that she told White and Farrow about the gift, both of whom assumed the stones were diamonds.
"One of the two said 'that is obviously Charles Taylor' and I said 'yes I guess it was'," she told the court, adding that she later gave the stones to Jeremy Ratcliffe, a representative of a Mandela charity.
Ratcliffe, the trustee of Nelson Mandela's charity in South Africa, issued a statement on Friday saying that following Campbell's testimony the previous day he had handed over to authorities three alleged "blood diamonds" given to him by the model.
Musa Zondi, a spokesman for the special investigations unit of the South African police, confirmed the authenticity of the diamonds.
"They are real diamonds, handed back to us now, and the investigation begins," he said.