Edward de Bono was famous for his unconventional methods of solving problems. He invented the term in 1967.

The publication of De Bono's final work, his last will and testament, has posed several unexpected questions that might test the most creative mind.

De Bono, who was assumed to be a very wealthy man due to the success of his self-help empire and international network of courses, died last summer in his native Malta at the age of 88 with less money than expected.

The author of 68 books asked his lawyers to make sure that his former co-author, the chief executive of his foundation, wouldn't benefit from his estate.

When his will was released last month, it was revealed that his estate had just over $13,000 in it. Despite being referred to as a one-man global industry and having institutions and foundations set up under his name, the philosopher's personal fortune appears to have been a myth.

Edward de Bono in a tie and button-down collar shirt holding his book Lateral Thinking in 1974

De Bono in 1974 with a copy of his book Lateral Thinking. Photograph: Radio Times/Getty Images

At school, De Bono was nicknamed "Genius" and won a Rhodes scholarship to study for a master's degree in psychology. His genius was as much for marketing as it was for his counterintuitive theories.

He retired to his family home in the Maltese town of Rabat. His works include The Use of Lateral Thinking, Parallel Thinking, Six Thinking Hats, and Six Action Shoes.

He had an idea that Marmite could be used to solve the Middle East conflict. The pots of spread were believed to be the solution to the antagonism between Arabs and Israelis. De Bono believed that eating yeast extract could bring about peace.

He once said that mine is a rare and unlabelled profession.

The Love of Two Cockroaches was his first and only literary approach to questions of love and lust. The book was written by Bartoli and was about a conversation between two ordinary roaches. The suggestion was that these insects are capable of emotional attachment and attraction. 12 years later, it is clear that there was a split.

Book cover of The Love of Two Cockroaches by Edward de Bono

The book written with Daniela Bartoli, de Bono’s philosophy student and later CEO of his foundation. De Bono ‘expressly excluded’ her from his estate. Photograph: Mint Editions

The clause in De Bono's will excludes Bartoli from benefiting from his estate. According to her business profile, Bartoli worked as De Bono's executive assistant for 14 years. The Observer couldn't reach her.

According to De Bono's will, he intended to give his former personal assistant a retirement gift of 350,000 dollars.

De Bono said that he looked upon her as his general manager. She is calm and low key. My life would be more frenetic if she were not.

Hills said she was always on call. This isn't a nine-to-five job and the days just blend in, but I enjoy it and I am glad to have provided the continuity.

There is uncertainty about what De Bono's various legatees may receive after the gift to Hills.

The identity of his children is included in the will. De Bono was thought to have had two children, but his will names four. His limited remaining estate will be shared between his two sons, Charles de Bono and Caspar de Bono, as well as another son, Edward de Bono, who is also known as Edward de Bono, and a daughter, Juliana Pars. The daughter of Donna Pars is studying at Cambridge University.

The will adds to the mystery of the author's life. She warned Piers Dudgeon that he wouldn't be able to hold the butterfly for her through her research. You won't be able to get a neat order around him.