Christina Aguilera Pens Note About "Stigma" Surrounding Aging as She Turns 40

Nothing can bring Christina Aguilera down today.

The "Beautiful" singer celebrated her 40th birthday on Friday, Dec. 18 by sharing a heartfelt note to Instagram about embracing the aging process.

"Dear 40, What a beautiful concept... to not only be 'turning' 40, but to be ARRIVING at 40!" she wrote. "This ever-present social stigma exists around getting older, but I have ALWAYS embraced it! I am forever an old soul and I appreciate the wisdom, grace and beauty that comes with each new year of life."

Acknowledging that it's been a "whirlwind of a year," Christina shared that now is the time to make difficult but important choices.

"I've heard it said that some of your best life is lived in your 40's," she continued. "You stop giving a f--k about all the bulls--t... clarity comes over you, and a new intention sets in with every move you make. I truly believe the best is yet to come and I am READY for it."

Christina Aguilera's Best Looks

The alum of The Voice also expressed appreciation for her 12-year-old son Max, who she shares with ex Jordan Bratman, and 6-year-old daughter Rain, her child with fiancé Matthew Rutler.

"To the rare and beautiful souls who have stood by me for over 20 years and counting, I am eternally grateful for you," the performer wrote. "I am blessed to have the most solid friends around me, a team I believe in that makes me feel supported and heard and of course, my family; my baby boy and girl, the most incredible children one could ever imagine! My heart is full."

In true Christina fashion, she concluded with, "So, 40, let's f--king do this. You have no idea what I have planned for you. I hope you're ready."