John Mayer and Katy Perry are apparently keeping their engagement a secret.

The brunette sparked rumours when she wore a diamond ring on her wedding finger to the MTV EMAs recently. Although it was claimed Katy sported the band because it went with her outfit, insiders are now saying she has in fact agreed to marry John.

John is believed to have popped the question just days after his brother Carl's wedding at New York's Mamaroneck Beach and Yacht Club on October 13. The singer-songwriter was best man and apparently made the decision to get down on one knee after realising how proud his father was to see Carl get married.

"John loved being part of the day and seeing how happy it made his dad. His father adores Katy and at the wedding he told her how special she was and how he'd love to see them settle down," a source told British magazine Grazia.

The stars have been dating on and off for around 16 months, with Katy previously revealing she is "madly in love" with the musician.

John, 36, is believed to have proposed with a vintage diamond ring that belongs to his family. However, 29-year-old Katy is apparently currently designing another ring which she will wear when the engagement is made public.

"It's top secret at the moment but it won't be long before it is official," a source promised.

Katy was previously married to Russell Brand, but the British comedian filed for divorce after just 14 months in 2011.