The mystery woman at the center of JADA and WILL SMITH’s marriage is a top-tier fashionista who knows ALL their intimate secrets!

Fawn Boardley is a longtime friend and “style director” for the A-list couple and their talented brood – and if Will and Jada split up, sources say the 43-year-old stylist could become an important witness in an epic divorce battle.

“No one knows exactly how much Fawn knows, but she’s become like a family member,” a Hollywood source said.

“She’s close to both Will and Jada, as well as their kids. If Will and Jada do split, Fawn could be caught in the middle of what may turn out to be one of Hollywood’s biggest divorce scandals ever!”

Fawn has been a regular presence during the couple’s 14-year marriage, which has been plagued by gay rumors and questions about their ties to the controversial religion Scientology, the source said.

“Fawn probably knows what’s gone on behind the scenes with Will and Jada,” the source pointed out. “If a divorce turns nasty, she very well could be pitted by one side against the other. Fawn could end up being the woman at the center of the divorce!”

And if she’s called to testify, Fawn – who was Jada’s personal assistant on the 2004 thriller “Collateral” – will have to take the stand, according to a leading divorce lawyer.

“What she knows IS fair game,” New York attorney Raoul Felder who is  an expert on celebrity divorces, told The ENQUIRER.

“Even if it’s something that happened 10 years ago, it doesn’t matter. In addition, if Fawn has kept diaries, letters, logs or e-mails, they could all be subpoenaed.

“For a divorce lawyer who wants to confirm something or expose a secret, this woman could be the music to their lyrics.

“She’s been in the middle of this marriage for a very long time, and she would be extremely valuable to either the husband or the wife in divorce court.”