Rumour has it the star revealed all at a dinner thrown by Martha Stewart at her East Hampton estate on Saturday.
The wedding venue is being kept secret, but it is expected the Captain America star will either marry in her fiance's native Paris, or in the Hamptons, where they have been spending most of the summer.
Scarlet - who split from ex husband Ryan Reynolds in 2011 - previously said she would probably "wing it" on her wedding day.
Story continues below
"I don't plan anything. I'm terrible at planning. Yeah, I'm not gonna plan anything - I like to wing it!"
Talking about her previous marriage and her new relationship she also confessed she finds it easier dating someone out of the limelight.
"It is [easier to be with someone who isn't famous], but it's more than that we do different things," she said.
"He's [Romain] in the whole art-scene world. So it's nice, because we can enjoy each other's worlds, but we don't have our crazy conflicting schedules and all that other stuff to contend with."
LOVE SCARLET? See more from her in the gallery below.