Christina Aguilera considers motherhood to be her "ultimate accomplishment" in life.

The 42-year-old singer has taken to social media celebrate her daughter Summer Rain's ninth birthday, and to reflect on her personal experience of motherhood.

Alongside some throwback photos of her daughter, the 'Genie in a Bottle' hitmaker - who Summer with her fiance Matt Rutler - wrote on Instagram: "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. [stars emojis]

"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. Mommy loves you so much! (sic)"

Christina previously opened up about her experience of motherhood, revealing that she prioritises her kids over her music career.

The chart-topping singer - who also has Max, 15, with her ex-husband Jordan Bratman - explained that she wanted to create a "stable" environment for her children.

During a 2019 interview with Haute Living, she shared: "I think of my kids first, always. 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."

Christina actually hesitated about joining the judging panel on 'The Voice'. But ultimately, the job really suited her and her family life.

She explained: "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 Los Angeles and in a place where I can focus on my kids.'"