It’s Rihanna. Of course!
We already know that RiRi, for the most part, does (and posts) whatever she wants. This includes, but isn’t limited to, smoking with Snoop, not wearing pants, and apparently a little bit of old-fashioned matriarchal boob-grabbing.
She explains the grab in a caption on Instagram, saying, “She's my rock so I hold on to she tight!!!”
That’s one way of looking at it! The singer was going through a little bit of a platonic boob-grabbing (and fan-groping) phase around then, anyway, so we suppose it doesn’t hurt. However, we’re not sure her grandma, who was on the other side of Rihanna’s mother in the original photo, approves.