The little girl arrived into the world on Monday night, according to the Sun.
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James Corden and Julia have welcomed a baby girl named Carey
James, 36, and Julia are already parents to a three-year-old son named Max. A spokesperson for the couple confirmed in May that they were expecting their second baby.
"James and Julie have loved every minute of becoming parents to their toddler Max, and were keen to give him a brother or sister who is close in age," a source told the Mirror at the time.
"They're delighted to be pregnant again and can't wait to expand the family."
James and Julia met in 2009 after being introduced by mutual friend Dominic Cooper. The actor popped the question on Christmas Day in 2010, and the couple tied the knot at Somerset's Babington House in September 2012.
The couple's son Max was born in March 2011
The new little family will soon be starting a new American adventure together, when James heads Stateside as the new host of The Late Late Show.
The star is replacing Scotland's Craig Ferguson - who is leaving after a ten year stint - in a deal reportedly worth around $8million (just under £5million). His first show will air on 9 March.
Following the announcement, James said, "I can't describe how thrilled and honoured I am to be taking over from the brilliant Craig Ferguson.
"To be asked to host such a prestigious show on America's number one network is hugely exciting. I can't wait to get started and will do my very best to make a show America will enjoy."