(PHOTO) Instagram: @badgalririRihanna poses for a photograph

Rihanna is celebrating a milestone birthday after turning 25 on Feb. 20 and the Bajan singer was sure to thank God on the special day.

The "Diamonds" singer shared a series of "throw back" birthday photos with her 29 million Twitter followers on Wednesday, including one of her and boyfriend Chris Brown which was taken on her 20th birthday. She thanked God for "His endless mercies."

"#throwbackRiRi my surprise 20th birthday party!! Im an old b---- now! Thank God for His gifts and His endless mercies! #25 #MilestoneLife," Rihanna tweeted Feb. 20.

(PHOTO) Instagram: @badgalririRihanna celebrates her 25th birthday, shares "throw back" photo

Friends and fans, including Rihanna's best friend Melissa Forde, took to Twitter to wish the singer a happy 25th birthday.

"Happy Birthday to the BEST BFFF @rihanna May God continue to bless and guide you. Loverrrr uuuuu…," Forde tweeted.

"Happy Birthday Rihanna!!!!!! Sends u LOVE and happiness.. @rihanna #PoItUpPoItUp #cakecakecake," rapper Trina tweeted.

"Happy Bday to my idol Riri! In honor I will listen to your music all day. You are so inspiring, love you always," fan Clarice Tan tweeted.

The 6-time Grammy award-winning singer has a lot to celebrate on her big day, particularly the success of her seventh studio album "Unapologetic," which debuted at number one in the U.S. on Nov. 19, 2012.

Her rekindled relationship with Brown, 23, is also said to be going strong however despite the happy occasion, Rihanna could not help but remember her late Grandmother Clara "Dolly" Brathwaite on her birthday.

"Missing you today especially #grangranDolly my guardian angel," the birthday girl tweeted.

In the months leading up to Brathwaite's death in 2012, Rihanna shared heart-wrenching photographs on Twitter of her beloved grandmother who appeared frail and evidently ill. She was receiving medical treatment at the Memorial Sloan-Kettering Hospital in New York City although she eventually passed away in June.