[3] During her youth, Teresa sometimes lived and studied in the household of her grandfather, Lorenzo Da Ponte, the noted music teacher, who had worked as Mozart's librettist on such masterpieces as The Marriage of Figaro.

Young Sickles also moved into the Da Ponte home; he left after about a year when his mentor suddenly died but maintained close ties with the family, possibly to continue the study of French and Italian.

Teresa's family relented and the couple married again, this time with John Hughes, Catholic Archbishop of New York City, presiding.

[6][7] In 1853, Sickles became corporation counsel of New York City, but soon resigned to serve as secretary of the U.S. legation in London under James Buchanan, by appointment of President Franklin Pierce.

The Sickles hosted formal dinners every Thursday, and Teresa was "at home" (available to callers) to other society ladies every Tuesday morning.

[10] She was especially celebrated as a hostess who was capable of charming the most sophisticated guest and making the most socially inexperienced feel at home.

Dan Sickles eventually received a poison pen letter[12] informing him of his wife's infidelity[13] and investigated further.

He discovered the allegations were true, and that Teresa and Key had rented a house for their assignations; it was located within walking distance in a poor, mixed-race part of town.

A few days later, on Sunday, February 27, 1859, Sickles saw Key outside his house, located on the west side of today's Lafayette Square, signaling Teresa with a handkerchief.

During the Civil War, he was commissioned as a Union general, receiving the Medal of Honor decades after he lost his lower right leg during the Battle of Gettysburg.