"We are thrilled to announce Adelina Rose Mariano 12:51am June 20th, 2014," Rob tweeted of his new baby girl on Friday. "Mom and baby are doing great! #4for4."
In a photo Rob posted on Twitter, he's smiling with Amber as she's holding their newborn child in her hospital bed.
In a subsequent tweet, Rob captioned a photo of his three daughters looking at their baby sister in her little bassinet, "Lucia Rose, Carina Rose, and Isabetta Rose are beyond excited to welcome their new sister Adelina Rose!"
Rob and Amber's three other daughters are between the ages of 2 and 4, one year apart from one another. All four girls share the same middle name Rose. Rob and Amber -- formerly known as Amber Brkich -- welcomed Isabetta in May 2012, Carina in December 2010 and Lucia in July 2009.
After appearing on their own original Survivorseasons, Rob and Amber met when they each returned to compete on Survivor: All-Stars in 2003. They ended up in the Final 2 together but Amber walked away with the $1 million via a 4-3 jury vote. Rob proposed to her during the May 2004 live season finale just after Amber won the game, and they went on to wed in April 2005. The wedding aired as a special on CBS entitled Rob and Amber Get Married.
Also in 2005, Rob and Amber competed as an "Engaged Couple" in the seventh edition of The Amazing Race and they finished in second place.
Rob and Amber later returned to The Amazing Race as "Newlyweds" for its 2007 all-stars installment. While they set a record at the time for finishing the first three legs in first place, they were eliminated during the fourth leg of the Race.
Between their two appearances on The Amazing Race, the couple filmed a short-lived show for the Fox Reality Channel entitled Rob and Amber: Against the Odds. It aired in 2007 and ran for 10 episodes.
Rob then gave Survivoranother shot in the show's twentieth season in 2010 dubbed Survivor: Heroes vs. Villains. He competed on the villains' tribe and was the eighth castaway voted out of the game. Rob was subsequently crowned the champion of Survivor: Redemption Island in 2011.
Rob has also been involved with several other reality TV projects along the way.