The handsome actor, 35, and his beautiful wife Lia Smith welcomed a baby girl last week.
The good news was confirmed yesterday (20 April) by US Weekly.
Justin and personal fitness trainer Lia got engaged a year ago in May 2013 during a holiday in California and got married in January in Hawaii.
Lia was already at least five months pregnant when she walked up the aisle in the romantic ceremony, but the newlyweds didn't confirm the news.
She reportedly gave birth to the couple's first child last Sunday (April 13).
Justin, who stars as Doug Billings in all three Hangover films, previously dated Ashley Olsen for two years before the couple split in 2011.
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Copyright: Rex Features WENN/Matthew Taylor/Daniel Deme/Josiah True/Matthre Taylor/Joe