Nicole made the announcement Monday on "The Late Show with David Letterman."
A source confirms to Usmagazine.com, “Nicole and Joel are in the process of planning the wedding. She’s very involved in every detail. She’s thrilled.”
The couple is expected to tie the knot in the summer. Richie and Madden started dating in December 2006 and have two children together Harlow, 2, and Sparrow, 5 months.
Last year, Nicole told CNN's Larry King that she was in no rush to make it official with Madden.
"I think for both of us, we are going to do it because we want to, not because that's what you do," said Richie. "We're going to do it when the time's right."
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