The French businessman -- half-brother of former French president Nicolas Sarkozy -- recently popped the question and the child star turned fashionista said yes, according to UsWeekly.
The news follows reports late last year that Olsen had been seen appraising Neil Lane engagement rings.
An insider said at the time, "Charlotte certainly won't want her kids to be around Mary Kate, who has a history of wild partying …"
But the duo has only grown closer since, even being spotted out on family days with Sarkozy's young daughter, who awkwardly towers over the diminutive Olsen.
Sarkozy divorced Charlote in 2010 after thirteen years of marriage.
Do you think she's finally found The One? Let us know in the comments!