An exiled Russian oligarch called Chelsea Football Club owner Roman Abramovich a "bastard" after being "blackmailed", a High Court judge was told.
Businessman Boris Berezovsky was "outraged" after a meeting with the Russian billionaire in France 11 years ago, Mrs Justice Gloster heard.
Mr Berezovsky's "long-standing partner", Elena Gorbunova, told how she recalled the aftermath of the meeting, in Cap d'Antibes in December 2000, in a written witness statement presented to the judge.
Mr Berezovsky, 65, is suing Mr Abramovich, 44, for billions of pounds at a Commercial Court trial in London.
He says the Russian billionaire businessman "betrayed" him and "intimidated" him into selling shares in Russian oil company Sibneft for a "mere 1.3 billion" US dollars - (£800 million) - "a fraction of their true worth".
Mr Berezovsky alleges breach of trust and breach of contract and is claiming more than £3 billion in damages - more than five billion dollars.
Mr Abramovich denies the allegations and denies that Mr Berezovsky is entitled to damages.
He says Mr Berezovsky was paid millions of pounds for his services as a "political godfather" but was not a business partner.
Mr Berezovsky alleges that Mr Abramovich "intimidated" him into selling shares in a number of companies after he left Russia in 2000, following a fall-out with then President Vladimir Putin.
Ms Gorbunova, who comes from Moscow and is 44, told how she "started dating" Mr Berezovsky in 1991 and had been his "long-standing partner" since the early 1990s.
She said she remembered that after the meeting in France in December 2000, Mr Berezovsky told her that Mr Abramovich was "blackmailing" him into giving up his interests in a Russian company.
"I remember that after the meeting, Boris was outraged," she said, in the written witness statement. "I remember Boris saying that Roman was a bastard."
She said Mr Berezovsky held a party to celebrate his 55th birthday in January 2001 but Mr Abramovich was not invited.
"He was never again invited to any of our parties," said Ms Gorbunova. "Boris never wanted to see him again."
She said she "understood" that Mr Abramovich denied meeting Mr Berezovsky in December 2000 but added: "I am sure that Roman is wrong about this. Although, I do not remember the precise date of the meeting, I can picture it very clearly."
Ms Gorbunova said Mr Berezovsky and Mr Abramovich "were friends" and she was "good friends" with Mr Abramovich's ex-wife Irina.
She said the two families holidayed together and attended birthday parties.
The hearing continues.