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Did Nicole Richie and Joel Madden celebrate the arrival of bouncing baby boy Sparrow by getting hitched?

That rumor comes courtesy of Radar Online, which claims the couple, who are also parents to button-cute 21-month-old daughter Harlow, got a marriage license last week and said "I do" in a "top secret ceremony" on Wednesday.

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Nicole's rep didn't respond to our request for comment on the knot-tying rumblings, but an insider tells Radar that the former party girl-turned-hands-on mom has been "talking more seriously" about making things legal since the August death of her onetime fiancé, Adam "DJ AM" Goldstein.

Adding to the speculation: TMZ reports Sparrow's birth certificate only contains the name "Madden," not "Richie Madden," like Harlow's.

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This time last year, Richie hinted to People magazine that an aisle-walk would eventually take place, and it wouldn't be "top secret."

"When we get married, everyone will know," she says. "It will happen when it happens."

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Lawfully wedded or not, the pair, who began dating in 2006, already has the married-with-children routine down.

"[Joel] has lost his hearing. Been asking 4 help round the house for 3 hours," Nicole tweeted on Thursday. "Wait, just said baseball & he's back! ITS A MIRACLE!"

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