The American's Got Talent host, 33, who recently revealed he and his wife of six years have been living separately for a few months, is said to have tried to make amends for speaking "out of turn" about their private marital issues by suggesting they seek couples therapy.
But a source told E! News that the Fantasy singer, 44, is currently preparing to file for divorce, saying: "She's getting all of her ducks in a row."
The insider explained she was caught off guard and "devastated" when Nick announced "there is trouble in paradise" and doesn't want to be blindsided again.
The former couple, who have three-year-old twins, Moroccan and Monroe, have an ironclad pre-nuptial agreement, which includes a custody arrangement for their children.
A source previously said the duo, who got married in 2008, have already agreed that Mariah will be the one to officially announce their divorce, as she is "done taking a passive role" in their split.
The friend added: "She told him there would be one announcement about the divorce and it was going to come from her team.
"Nick said he was fine with this too. He knows he really upset her by speaking out of turn last week and has apologised for it."