The actress’ lone appearance follows rumours Millepied, a ballet dancer and choreographer, had become romantically involved with climate change activist Camille Etienne.
The rumours were first sparked by French magazine Voici, which published images of Millepied and Etienne, 25, meeting up in his office. The pair were snapped entering the building separately then, two hours later, leaving 10 minutes apart.
The magazine also claimed Portman had been aware of her husband’s cheating for several months.
According to Page Six, the couple, who met on the set of the dance film Black Swan, separated last year but had been working on their marriage.
“They have not split and are trying to work things out. Ben is doing everything he can to get Natalie to forgive him. He loves her and their family,” a source told the news outlet.
The source also said Portman is known to be “incredibly private” and “her biggest focus right now is protecting the kids”. She has a son called Aleph, 12, and a daughter called Amalia, 6.
The alleged split follows a string of Hollywood heartbreaks this year.
Last month, British popstar Ellie Goulding was reported to be taking a break from her four-year marriage to Caspar Jopling amid rumours the couple’s relationship is on the rocks.
In May, Kevin Costner was said to be left stunned when his wife of 18 years, Christine Baumgartner, served the star with divorce papers.
And in April, actor Shannen Doherty filed for divorce from her husband, Kurt Iswarienko, after 11 years of marriage.
