That's quite a diamond on Katy Perry's engagement ring finger.  The bauble made an appearance over the weekend on the red carpet of the MTV European Music Awards setting off a firestorm of speculation that John Mayer may have popped the question.

If the new sparkler is a gift from Mayer — engagement or otherwise — it would not be the first ring he’s given Perry. In February, he gifted her a one-of-a-kind heart shaped ruby from jeweler Daniel Gibbings, which she wore in the same spot.

Katy has publicly stated she hopes to keep her romance with John 'normal'.  But the two have not been coy about they're feelings for each other, even professing their love on a new duet called 'Who You Love'.

There have been no official engagement confirmations from either star's reps.