Is Katy Perry Wearing Engagment Ring from John Mayer?

Katy Perry hit the red carpet at the MTV EMAs wearing an elegant dress, but more eyes were noticing the ring on her hand. Not just any ring, but a diamond ring. Are Katy Perry and John Mayer engaged?

But multiple sources tell Us Weekly:

The piece of jewelry in question is not, in fact, an engagement ring.
"She's not engaged," the insider tells Us of John Mayer's girlfriend. "It was just a ring that went with the outfit." (Perry's rep doesn't comment on the singer's personal life.)

The ring in question:

Katy Perry at the MTV EMAs: