The Boy Is Mine hitmaker, who won a Grammy Award in 1999, is currently starring on Broadway in a production of Chicago, and she decided to give travellers on the Big Apple's subway a free treat.

The pop star was filmed by a pal as she sang Whitney Houston's Home on a crowded train, but she was left baffled when only one passenger responded and gave her some constructive criticism.

In a video clip posted on Brandy's official page, she is seen singing before turning to other travellers in the carriage and asking, "What y'all think thought of that? Y'all thought that was cool? Hello? Nobody heard me singing? Nobody cares? Okay."

She then faces her friend's camera and adds, "Nobody on the train responded and I feel very, very emotional right now."

However, one man then offered some words of advice but surprised the singer by explaining her behaviour was nothing unusual on the New York underground and she was too "into" herself to connect with others.

The man told Brandy, "We've seen this a million times. You have got to do something different."

After exiting the train at the next station, Brandy said, "I've got one fan on the subway."