"Dearest Ladies and Gentlemen, I would like to introduce our little girl Westlyn Reign Brolin (Bean)," he wrote of a video showing the newborn sound asleep, reports people.com.
"Mama Kathryn was stellar during this miracle birth and Bean is a flawless gem through and through. We are blessed to the core and appreciate so much the love and support during this pregnancy from all who have partaken in our journey, directly and/or indirectly," he added.
Brolin, 50, has two other children, Eden, 24, and Trevor, 30, from his first marriage to actress Alice Adair. His second marriage was to actress Diane Lane, with whom he had no children. The latter pair stayed married until 2013.
Boyd, 31, is the creator of Midheaven Denim, a line of jeans for taller women. The 5'11" new mother is also a model and was Brolin's personal assistant before the two became engaged in 2015. The couple married in 2016.
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