new tattoo is close to her heart ... both figuratively and literally.

The 24-year-old singer took to Twitter last night to reveal her latest body ink ... and its very revealing location.

Her 17th (by our count) tattoo: The Egyptian goddess Isis, who sits just below the singer's breasts.

"Goddess Isis- Complete Woman - Model for future generations- #GRANGRANDOLLY - always in and on my heart," Rihanna tweeted about her new tatt.

She got the ink in memory of her late grandmother Clara "Dolly" Braithwaite, who passed away earlier this year.

Rihanna's other tattoos include a giant falcon on her ankle, stars on her neck, a gun on her ribcage, music notes on her feet and the word "Love" on her finger.

Check them all out in the gallery above!

Hot Videos