Guerilla graffiti artist Banksy has helped to raise $615,000 (£410,000) to aid the homeless after donating a painting to a New York charity store.

The enigmatic British star purchased a $50 (£33) oil painting of a mountain scene by obscure artist K. Sager from the Housing Works Thrift Shop in Manhattan's Gramercy neighbourhood weeks ago, and quietly returned it on Tuesday (29Oct13) after adding a Nazi soldier admiring the scenery.

Josh Haskins, the store assistant manager, says, "Someone showed up at the counter and told a volunteer to get the manager, saying, 'A valuable piece of art is here.' He then just walked away."

Bosses soon realised the 'vandalised' image was the work of Banksy, who staged an art residency in New York for the month of October (13), and their suspicions were confirmed after he shared a photo of the updated painting on his official page.

They placed it up for auction online and the piece sold for $615,000 on Thursday (31Oct13).

Charity executives plan on using the funds to continue its mission of fighting homelessness and Aids.