Katy Perry played the dutiful girlfriend by mingling with John Mayer's family at his brother's wedding over the weekend (12-13Oct13).

The I Kissed a Girl hitmaker was in attendance for the nuptials of Carl Mayer and his fiancee Shera Adika at Mamaroneck Beach and Yacht Club in New York on Sunday (13Oct13).

Perry joined Mayer's relatives to watch as the pair exchanged vows while the singer/songwriter acted as best man.

A source tells New York Post gossip column Page Six, "They were very polite and down-to-earth and didn't want to take away from the bride and groom's day.

"Katy stayed behind the scenes and politely turned down photos. It was a beautiful ceremony on the water."

The wedding was held almost three years since Perry walked down the aisle with Russell Brand in India on 23 October 2010. They divorced in 2011.