English writer Charles Dickens branded his own father a "jackass" for his recklessness with money, according to a newly-discovered letter.
The 172-year-old, unpublished letter is expected to sell for 3,000 pounds at an auction in London on November 13.
The novelist fell out with John Dickens after his father racked up huge debts so he could lead an extravagant lifestyle beyond his means.
Dickens senior regularly used his son's fame as an excuse to borrow money from his publishers and solicitors, with the author often having to pick up the bill, the Daily Mail reported.
By 1840, the problem got so bad that Dickens sent his father and mother Elizabeth to live in Devon to keep him out of trouble.
At the time the writer even took out adverts in newspapers to say he would no longer be paying off his father's debts.
But a letter that has now come to light after 172 years shows that John Dickens carried on borrowing money - and Dickens carried on bailing him out.
On August 17, 1842, the writer wrote to his solicitor Thomas Mitton in reply to letter asking him to pay off some of his father's debt.
Lambasting his father, Dickens wrote: "I think my father is a great Jackass - which is not a novel sentiment with me, by any means.
"I am rather horrified by your statement... I fear... that I have very little money and I did not expect you to come down upon me so soon," he wrote.
Signing off he promises to have dinner with him soon when he will "bring a blank cheque".
"This letter is further evidence of the appalling trouble Dickens had with his father who was very reckless financially," Michael Slater, a Dickens' expert, said.
"By 1841 Dickens was so exasperated that he told Mitton to put an advert in all daily newspapers saying he would not be responsible for any debts incurred by his father," he said.
"But this letter does show that was not the case privately and also shows how bothered Charles Dickens was by his father's debts," he said.
"Clearly Dickens had been expecting to pay but was surprised by how much money Mitton had given his father without him knowing. He is saying in the letter what a fool he is," Slater said.
Despite their strained relationship, Dickens and his father remained on good terms and the novelist even used him as inspiration for the character Mr Micawber in his 1850 work David Copperfield.
The letter has emerged after being put up for sale at auctioneers Bonhams by a private collector.
"The fact that the letter is newly discovered and unpublished is very exciting and makes it extremely desirable," Francesca Spickernell, from Bonhams, said.