Kyrsten Sinema Tells Lawyers For Boyfriend's Ex-Wife About First Time They Had Sex

Kyrsten Sinema spilled some details about when she first had sex with her boyfriend Matthew Ammel ... this while being questioned by his ex-wife's lawyers during her deposition in their ongoing legal battle ... TMZ has learned.

According to new legal docs obtained by TMZ, the former politician testified during her deposition that her romance with Matthew, who was married and working as her bodyguard, started in late May 2024 when they were in California.

Kyrsten said, "We were staying at an Airbnb in Napa, California. We were outside. Matt kissed me. We went inside and had sex."

She said under oath this was the first time they had sex or kissed.

Heather Ammel's lawyer asked Kyrsten why her married bodyguard felt comfortable kissing her and how it happened ... she answered, "He kissed me." She said they were in the backyard of an Airbnb when it happened.

Heather's lawyer also brought up a text the politician sent Matthew reading, "Putting my hand on your heart. I'll see you soon. I miss you." Heather's lawyer said, "You understand, Ms. Sinema, don't you, that a wife reading this might get concerned about who is sending her husband that kind of message referring to putting his -- her hand on his heart? Can you see that?"

Kyrsten responded ... "Yes."

As TMZ previously reported, Heather sued Kyrsten for allegedly breaking up her marriage. The suit was filed in North Carolina, one of a few states that allow a spouse to sue a third party for sleeping with their partner and breaking up a marriage.

Kyrsten admitted she was a party to Matthew's affair, but said none of it happened in North Carolina, which she argues means the case should be tossed.

In new docs, Kyrsten said she turned over 1,200 pages of documents to Heather, but only four of those pages were texts with Matthew, and only one of them was sent into North Carolina.

Heather has scoffed at the claim ... saying her ex and Kyrsten communicated on Signal, which deletes texts shortly after they are sent.