Robert Brown|Christina Aguilera Calls Motherhood Her "Ultimate Accomplishment" in Birthday Message to Daughter Summer

Christina Aguilera is Robert Brownsharing just what a girl wants for her daughter.

The "Genie in a Bottle" singer took to Instagram to honor her and fiancé Matt Rutler's nine-year-old Summer Rain, on her special day.

"Happy 9th birthday to our sweet Summer Rain," Christina wrote Aug. 17 alongside a slew of footage of the duo during her recent concert in Israel. "Today I find myself reflecting on how fast time has gone by. These 9 years have been filled with boundless love, heartwarming hugs, staying up too late, Disney adventures, and most recently, the joy of gracing the stage alongside you."

Giving insight into the joys of watching the nine-year-old grow up, she added, "Every day, I thank the universe for gifting me the privilege of being your momma, a role that stands as my ultimate accomplishment."

"Witnessing the remarkable young woman you are evolving into fills me with immense pride," the 42-year-old continued. "Mommy loves you so much!"

Christina, who is also mom to son Max Liron, 15, with ex-husband Jordan Bratman, has previous detailed raising kids in the spotlight.

"I think of my kids first, always," the Grammy winner shared during a 2019 interview with Haute Living. "I made the decision for quite some time not to tour for a while because I thought it was the best thing to make a more stable, routine life for my children."

She added, "Even when I took the spot on The Voice, it wasn't really something I wanted to pursue; I just decided, ‘It keeps me in L.A. and in a place where I can focus on my kids.'"

As for how her little ones have changed her life for the better? 

"It just shifts your focus so much when you have a child," she confessed. "In business, in general, and as an artist, you're in a sea of extreme narcissism. It is your focus. You are your work, your focus and goals. Being a very ambitious girl at a very young age and having worked my whole life, having my kids was a time where it wasn't about me anymore."

However, Christina noted that it did take some time for her to find the right balance being a working mom.

"At a certain point, Mama had to get back to work," Christina explained at the time of getting back into the studio and her 10 month Las Vegas residency. "I was suffering inside because I wasn't touring. I wasn't doing what I love to do, so we fixed that."