Caitlyn Jenner's Daughter Cassandra Jenner Marino Gives Birth to Baby Boy

Cassandra's brother, Burt Jenner, welcomed a baby boy in July.

Caitlyn Jenner has a new grandson!

The I Am Cait star's daughter, Cassandra Jenner Marino, gave birth to her third child, a baby boy, on Tuesday.

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"He made it! One day before his due date and on Mike's dad's birthday. 8lb 13oz 22 inches long," Cassandra wrote on Instagram. "I am elated and exhausted but a super happy non-pregnant mama :)."

"Proud big sisters. They are over the MOON," she captioned another pic of her daughters, Isabella and Francesca, getting a good look at their new baby brother.

WATCH: Caitlyn Jenner's Son Burt Welcomes First Child

Cassandra, 35, is Caitlyn's daughter from her first marriage to Chrystie Crownover -- and has admitted to growing closer to Caitlyn since her transition.

"My relationship with Caitlyn is much better than with Bruce, but we still have a lot of work to do," she told People last year. "We didn't talk for years, and now we see each other every couple of weeks and talk on the phone, which I am grateful for."

"She's happier and more appreciative of her family," she added. "She is trying harder, and there is a softness to Caitlyn that is new to me. I think part of that is that when someone is happier, they are just nicer."

Cassandra's newborn son is the second Jenner grandson to be born this year. Her brother Burt, 37, welcomed a baby boy named Bodhi in July.

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See more in the video below.