Johnny Manziel's Fiancee At War With Ex Involving FBI, Diamonds, Louis Vuitton

Before Bre Tiesi said "yes" to Johnny Manziel ... she was engaged to another man -- and the backstory involves everything from money to diamonds to the FBI.

Bre's ex-fiance is Chris Anzalone -- who was a BALLER in Southern California until he was arrested and convicted for running a $16 million investment fraud scheme.

But before he was sentenced to 15 years in federal prison, Anzalone showered Bre in riches -- including cars, designer purses, Rolex watches and a 10-carat diamond engagement ring.

Their relationship went sour when Chris was locked up -- and Anzalone claims Bre embezzled more than $1.3 MILLION in cash and expensive property.

Chris has lawyered up and demanded his stuff back -- but there's one problem ... Bre says he's lying and she doesn't have it anymore.

TMZ Sports spoke with Bre's attorney who says Tiesi met with FBI agents and surrendered every item she was asked to give up ... items the feds claim she received from Anzalone's ill-gotten fortune.

Bre says none of it was embezzled -- everything she had was given to her as a gift.

Bre's lawyers also provided documents to TMZ Sports showing a list of the surrendered items which include Louis Vuitton backpacks, designer luggage, watches and rings.

Bre's attorneys say Anzalone also accused Tiesi of letting Manziel propose to her with the ring HE used back in the day. But Bre's team provided receipts showing Johnny's ring was purchased in February.

Anzalone has fired off legal letters to Bre's team threatening a lawsuit. Bre's lawyers deny any wrongdoing and have this message for Anzalone ... BRING IT ON.

Guess Bre has a thing for bad boys ...