Nicole Richie has given birth to a boy.
The couple announced on Nicole's website: "In the middle of night, the very early hours of September 9, 2009, Sparrow James Midnight Madden was born. Nicole, Joel, Harlow and Sparrow are all doing well. Thank you for all of your good wishes."
Joel added on Twitter: "1st day of his life and my son is already a trending topic on twitter. That's right son, ur just like your old man. wait, i've never been a #TT (sic)."
Experts claim the couple's choice of name for their son show they are "free spirits" and also keen to given their child a fashionable moniker.
Baby name expert Pamela Redmond Satran said: "Bird names are definitely getting hotter. Of all the animal names, bird names are the hottest.
"It has a spiritual symbolism - they're seen as light, one with the sky and nature and in a more uplifting, positive way than other animals, like a fox, which is more macho.
"It's an interesting choice for a son because you really can't tell if it's a boy or a girl. Something we've started to see is parents being much more open to giving their sons names that have a feminine feel or are unisex."
Nicole, 27, and Joel announced they were to become parents again in February.
Joel, 30, spoke of his excitement at the impending new arrival last month, saying: "We're very, very blessed. We've already had one healthy kid, and that's all you can ask for as a parent - healthy kids."