Amanda Silverman, publicist for de Matteo, says Jennings proposed to the 37-year-old actress at his concert in Utica, N.Y., last Thursday.
Silverman says Jennings took de Matteo by surprise when he called her to the stage to pop the question.
The couple have an 18-month-old daughter, Alabama.
In an update on Twitter, Jennings says: "I'm a lucky man. I'll never forget Utica."
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