Nicole, 52, recently celebrated 13 years of marriage to country musician Keith, 51, while Alexander, 42, plays her character Celeste's abusive love interest Perry in the HBO's hit TV show Big Little Lies.
WATCH to see Nicole reveal her daughters will star in upcoming episodes of Big Little Lies:
But while the friendly display set tongues wagging, Nicole and hubby Keith put speculation to bed with a tactile display outside the haute couture show on the steps of the Petit Palais.
The Australian-born actress previously opened up about her close bond with Alexander, and caused a storm of controversy when she locked lips with her co-star after his Outstanding Supporting Actor win at the Emmys in 2017, Daily Mail Australia reports.
Clarifying the incident, Nicole spoke to W Magazine about the intensity of working on Big Little Lies.
"There were times on that set when it was intense. But he [Alexander] and I communicated.
"There had to be such safety, such honesty and such raw vulnerability there that we have a different connection.
"I mean, I'd kissed him many, many times [in character] on the set. So [the Emmy Awards kiss] was just my way of going...we were both shocked and we were like - oh my gosh, I'm so glad you won."
Nicole and Alexander's close bond was cemented as a result of the intense sex scenes and physically violent altercations between their characters.
Nicole looked age-defying in a black, strapless midi-dress covered entirely in sequins, which accentuated her tiny waist and trim pins.
The Golden Globe winner showed her sartorial skills by slipping an ivory, satin blazer over her shoulders.
Hollywood's golden girl teamed the ensemble with a fashion forward pair of kitten heel pumps and toted a small, black clutch.
The mother-of-four - who is mum to adopted children Bella and Conor with her ex-husband Tom Cruise, and biological daughters Sunday Rose and Faith Margaret - let her blonde locks hang straight and loose around the shoulders, and finished her look with a pop of ruby lipstick.
It was a star studded scene across the French capital with international celebrities flocking to the runway shows.
American actress Zendaya also attended the Giorgio Armani Privé show, while Celine Dion looked spectacular at the Alexandre Vauthier event.
Australian icon Margot Robbie was at the Chanel Fall 2020 show as part of her ambassadorship of the house, and Christina Aguilera attended the Jean Paul Gaultier fashion show.