Celebrity Parents John Stamos Sends Sweet Message to ‘Full House’ Costar Ashley Olsen on Birth of Baby Boy: ‘I Am Blessed’ The actor called watching Ashley and her twin sister Mary-Kate grow up "one of the greatest joys of my life" By Kirsty Hatcher Kirsty Hatcher Kirsty Hatcher is an Associate Editor on the People.com Morning Team. She has been working at PEOPLE since 2023. Her work previously appeared on ok.co.uk, in OK! Magazine and Reach PLC magazines. People Editorial Guidelines Published on August 25, 2023 07:59AM EDT Close John Stamos and Ashley Olsen. Photo: Todd Owyoung/NBC via Getty Images; Matt Winkelmeyer/Getty Images for YES 20th Anniversary Gala John Stamos is sending a sweet congratulations to his Full House costar Ashley Olsen on the birth of her baby boy. On Thursday, Stamos, 60, paid tribute to Ashley and her twin sister Mary-Kate Olsen, 37, and shared his well wishes to Ashley on becoming a mom in a post on Instagram. “Watching Mary-Kate and Ashley grow into the incredibly bright and remarkable women they are today has been one of the greatest joys of my life,” the post began. “If you would have told me those blue-eyed babies I met on set nearly 40 years ago would still be in my life at 60 years old, I wouldn’t have believed you. I am blessed.” Stamos concluded his post, “Congratulations to Ashley and her husband, Louis, who welcomed their baby boy last week.” The post featured a compilation of clips of Stamos spending time with Ashley and Mary-Kate on the Full House set, trips to Disneyland and the beach and partying at events with the siblings as adults. John Stamos Celebrates Turning 60 With Birthday Wishes From Wife Caitlin McHugh, 'Full House' Stars and More In a sweet touch, Stamos included a voiceover in the clip from a section of the audio version of his new autobiography, If You Would Have Told Me: A Memoir, released Oct. 24. The actor recalled Ashley and Mary-Kate being cast as one of the daughters in Full House, Michelle Tanner, and how his relationship with the twins developed over the years. “The last casting call is for Danny’s little daughter,” said Stamos, who played Jesse Katsopolis in the ABC sitcom, which ran from 1987 to 1995. “Two adorable munchkins, Mary-Kate and Ashley Olsen, are cast in the role of Michelle. They have big blue eyes wide with wonder.” Stamos continued, “Right away I know the relationship between Jesse and Michelle is an important one, but as the show develops the connection grows. I’m young but I really want kids someday and these lovely little girls so bouncy and bright represent the best versions of future dreams. They allow me to consider fatherhood like a benched baseball catcher in a dugout, watching from afar but not having to catch any curve balls.” John Stamos with Mary-Kate and Ashley Olsen. John Stamos/Instagram Ashley Olsen Welcomes First Baby with Husband Louis Eisner The You star went on to say that the siblings became “the kid of humans I hope to have one day.” “I take them to Disneyland, I adore them, giving them kisses on top of their head, buy them a few crappy souvenirs and then hand them back to their parents to do the hard work,” he said. “The little kids that were supposed to be background noise grow up to become the kind of humans I hope to have one day. They are precious, delightful and bright. I adore them.” John Stamos with Ashley and Mary-Kate Olsen at Walt Disney World. Mark Ashman Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories. Last week, PEOPLE confirmed that Ashley and her husband Louis Eisner, 34, had welcomed their first baby together, a son called Otto. No other details about the infant or his birth have been shared. TMZ was the first to report the news. Olsen and the artist married in a private ceremony in December 2022, PEOPLE confirmed at the time.