Pop superstar Rihanna started her birthday on a sombre note on Wednesday (20Feb13) by remembering her late grandmother.

The Umbrella hitmaker was left distraught when Clara 'Dolly' Braithwaite lost her battle with cancer last summer (12) and she subsequently had a tattoo of ancient Egyptian goddess Isis inked across her ribcage in her memory.

Rihanna turned 25 on Wednesday, and she took a moment to remember her grandmother by posting a picture of her on on her Twitter.com page.

In the accompanying post, she writes, "Missing you today especially gran gran Dolly my guardian angel."

The singer also posted a snap featuring her and boyfriend Chris Brown celebrating her birthday in 2008, and added, "Throwback RiRi my surprise 20th birthday party!! I'm an old b**ch now! Thank God for His gifts and His endless mercies!"