Two unmasked men stole Magritte's Olympia last week, after threatening staff at Magritte's former house in Brussels, reports the Guardian newspaper, United Kingdom.

The house is used as a tiny museum, which you can visit only by appointment.

The men inquired as to whether the museum had opened, which it had just 10 minutes previously.

The attendant had a gun put to her head and was made to kneel in the garden whilst the thieves made their getaway.

Magritte's Olympia depicts a side view of Magritte's nude wife Georgette, her blonde hair flowing over her shoulders, lying on her back and inspecting a sea shell on her stomach.

The title is a nod to Manet's Olympia, painted 85 years earlier in 1863.

That painting caused a storm, largely due to its being clear that the subject is high class prostitute (the animal featured in that is a black cat, which symbolises the fact, apart from anything else).

The work was painted whilst the Belgian surrealist was living in the house, which he did for 20 years, along with many of his most famous works. He also met up with many contemporary surrealists there.

He is most famous for his 'This is not a pipe' painting, along with the slightly eerie silhouettes and holes based on the shape of bowler-hatted men. Few of his works have been stolen.

It is difficult for thieves to make money from such paintings directly, as obviously they are too recognisable sell on the open market.

Thieves sometimes hold the paintings to ransom, but otherwise they are used in place of a debt payment or as collateral.

"The paintings either tend to turn up very quickly when the thieves realise it's a lost cause, or if they do go missing for a long time, they often change hands so many times that the final seller doesn't realise there is a problem with the painting." explained Maja Pertot Bernard of the Art Loss Register.