On Monday, Ireland Baldwin, 25, paid tribute to sister Carmen on Instagram, sharing a photo of Carmen snuggling with baby sister María Lucía Victoria, nearly 6 months, and writing, "Happy birthday, Carmen 💖 I know you don't have Instagram yet (thank God) but I love you with all my heart and when you do eventually get an Instagram in 5-10 years or whatever cooler app is available then, please follow me back. I'm not worthy. 👑"
In the comment section, Ireland's mother Basinger, 67, wrote, "Carmen…… such A beautiful twosome…… you are so beautiful…….
I love you 2 ….. together in this picture…… But YOU Know how to get it done and she will learn from you……..👏👏👏👏👏👏👏👏👏👏👏👏👍🙏🏻✨🥰🌈❤️🌸."
Alec shares Ireland with Basinger. They split in 2002 after nearly nine years of marriage, when Ireland was 7 years old.
He now shares six kids with wife Hilaria (whom he wed in 2012): daughters Carmen and MariLu, plus sons Rafael Thomas, 6, Leonardo Ángel Charles, 4, Romeo Alejandro David, 3, and Eduardo "Edu" Pao Lucas, who turns 1 next month.
Want to get the biggest stories from PEOPLE every weekday? Subscribe to our new podcast, PEOPLE Every Day, to get the essential celebrity, entertainment and human interest news stories Monday through Friday.
Sharing a photo of all six of her kids Monday, Hilaria wrote on Instagram, "Happy 8th birthday Carmen…we love you so…other than the babies, we almost got the photo all smiling 🤣 ❤️. Ps that's my hand under Edu's arm." She also shared a silly outtake from the group photo session.
"Divorce is hard on a kid, no matter how you cut it. And ours was very public and nasty, so I brought up Ireland in a very unconventional way," said Basinger at the time. "... I just wanted her to be free. If she wanted to have her friends over and write over the walls with pen, that was fine. I wanted her childhood to be full of love and light and animals and friends."
Though Basinger and Alec were embroiled in a four-year custody battle over their daughter following the split, she said they had since moved on and were on better terms. "[Alec and I are] cool now, though," she said. "Life goes on."
In April 2019, Hilaria told PEOPLE about her "great" relationship with stepdaughter Ireland.
"There's obviously things in the past … with her parents, they've suffered, and I don't get involved in that," she said at the time. "I think that's one of the smartest things I've ever done. I'm here, everybody knows that I love them and I care about them and if they need me I'm here, and I'm never going to put my nose where my nose doesn't belong."