Apparently the couple of three years and two children have had plans to wed for some time now but were keeping it under wraps until... one of them had an appropriate venue to tell the world?
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Who knows!? Seems more likely that they were waiting in deference to Casey Johnson's untimely death (the two girls where childhood friends, with Casey originally cast to play the part of Paris' BFF on The Simple Life before Nicole signed on). Casey Johnson Found "A Few Days" Dead
Shortly after Nicole scampered off set to NYC restaurant Abe & Arthurs all a-glow, her Twitter-happy fiancé stole Letterman's thunder:
Yep. i'm engaged. Very happy. Yeah we've been engaged for a while so your all kind of late on that. But Thanks for the hoopla all the same," he tweeted.
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Currently snowed-in somewhere in Manhattan, the Richie-Madden clan sure seems happy. Best of luck and congratulations!