The Kill Bill star and the French businessman have been embroiled in a legal wrangle over their four-year-old Rosalind, aka Luna, since 2014, after Busson went to court to demand regular access to his daughter following their split.

An initial deal was agreed in September, 2015, but the former couple has since fallen out again, with Busson objecting to Thurman's request to take Luna with her to Europe while she works on a movie.

The custody trial kicked off at New York's Manhattan Supreme Court last week (13Jan17), and on Friday, Thurman took the stand and opened up about her time with Busson, according to the New York Post's Page Six.

"He was very difficult to be with," she said. "He was very angry. He got meaner and meaner."

Uma and Arpad initially split in 2009, but they gave their romance another go.

She also spoke about a big fight the couple had after reuniting in 2009, when Thurman was forced to cancel a trip to the Bahamas following a serious bicycle accident her daughter with ex-husband Ethan Hawke was involved in.

"He had a very aggressive tantrum in front of all the kids, he started yelling and shouting throughout the house," she said. "It was very upsetting and traumatic for myself and the children."

The 46-year-old and Busson went through a few more break-ups before she became pregnant with their daughter in 2011. Thurman reveals her pregnancy news was not met with a happy response from Busson.

"He looked at me and said, 'Well the child won't share your last name, cannot be a U.S. citizen and can't have a U.S. passport and will be raised Catholic'," she testified.

Uma revealed the relationship was "terrible" from that point and they split for good in 2014. Thurman testified she "didn't hear from Busson for quite some time" after the break-up, but then his secretary "reached out and said that he wanted to have a visit with (our daughter)."

The former couple argued over the custody of their daughter and Busson subsequently sued her.

"When she doesn't see her father for a long time I think it just creates anxiety," Uma said about her daughter's relationship with her ex. "It seems like she's upset or something is bothering her around the whole issue."

The trial continues.