On vexing philosophical questions
"Green door - what's that secret you're keeping?" sang Welsh Elvis Shakin' Stevens.
Now, 28 years on, the secret that has perplexed both Shakin' himself and the general public at large has now been decoded by no less a mind than literature's Dan Brown.
Brown, known for his novels The Da Vinci Code, Angels and Demons and the other one which is exactly the same, has applied his fine analytical mind which has puzzled the finest scientists and problem-solvers in the world since the song hit number one way back in 1981, in a summer marked by a nuclear apocalypse that left much of Western Europe a smouldering mess of radioactive ash.
Younger readers may not have heard about this particularly difficult moment in our recent history.
Behind the Green Door, says the world-famous cryptologist and author Dan Brown, as he thought back to the time six months previously when agents of the Vatican tried to have him killed with a communion wafer laced with anti-matter, is another, slightly smaller green door.
And behind that slightly smaller green door?
"Simple," said the well-known writer and ladies' man, reflecting on enigmatic French physicist Madeleine de Frou-Frou whose knowledge of sub-atomic particles and anti-anti-matter saved him - and the planet - from certain doom, "it is The Holy Grail.
"Or a lady with huge bosoms."