“I've known him since we were in our early 20s. We went to dinner at a place in London called The Ivy with his then-girlfriend Liz Hurley and my sister and just a huge bunch of people and we just kind of clicked,” she began.
“My sister and I were speaking our secret language and Hugh was fascinated because my sister and I have this language that we can speak so we can be understood in a crowd and nobody can understand us.”
When asked for a little more info on what the language actually entails, the actress simply laughed and said it was “silly.”
“If I end up telling you then you'll be able to decode it,” she explained, adding that it was especially useful when the pair are out and about.
"It was really helpful when we were like at parties and they were and we had our boyfriends and stuff we would be able to use our language and they'd all be like 'What?'" she said.
In an interview with Entertainment Weekly, Hugh, 60, also reflected on the moment he met Nicole.
"What I remember most was that she was very nice, charming, but when she spoke to her sister, she spoke in a secret language," Grant recalled. "And I said, 'Excuse me, are you speaking in a secret language?' And they both said, 'Yes.'"
So, what does this secret language sound like, you ask?
"It's weird,” the actor shared. “It sort of goes 'eggy-peggy this, eggy-peggy that,' and they still do it ... I've always liked her, she's a silly Aussie girl."
The Undoing is currently being filmed in Australia and is expected to be one the most talked-about TV series of the year.
“The great thing about the series – and what really drew me to it – is that it’s so twisty and nothing is as it seems,” Kidman previously told WHO.
“Choosing to unknow things is a fascinating part of human nature – when and what you choose to believe and what you choose to see.”
As well as Hugh, Noah Jupe and Donald Sutherland will also star in the highly anticipated show.