“For no real good reason Nelson got it into his head that Troubridge was out to fix it that he remained at sea and away from Emma.”There is a letter that exists which Troubridge wrote to Nelson in August 1801, stating how hurt he was by what Nelson had said about him.”The letter is being sold by International Autograph Auctions in Marbella, Spain, on Saturday. The letter was written four years before Nelson was killed after leading the Royal Navy to a decisive victory at the Battle of Trafalgar.It has been in the possession of a private collector is now being sold for a pre-sale estimate of £15,000.Auctioneer Richard Davie said: “This is a letter of interesting content and good association.”Nelson had quite a ruthless streak in him, as reflected in this letter, and didn’t suffer fools.” “Who upheld him when he would have sunk under grief and mortification?…Nelson, that Nelson that he now Lords it over.”So much for gratitude. I forgive him, but, by God, I shall not forget it.”He enjoys showing his power over me. Never mind; all together it will shorten my days.”He signed off: “Ever my dear friend your affectionate half sea sick Nelson.” Admiral Nelson’s mistress Emma HamiltonCredit:BNPS The letter from Admiral Nelson to his mistress Lady Emma Hamilton in which he launches a bitter broadside at a superior officerCredit:IAA/BNPS Andrew Baines, a Nelson expert and head of historic ships at the National Museum of the Royal Navy, said Nelson’s relationship with Troubridge became fractious after Nelson’s affair with Lady Emma Hamilton.Mr Baines said: “Troubridge took a dim view of the relationship as did the vast majority of the establishment.”It wasn’t so much that he had a mistress, but the issue was this menage-a-trois Nelson was involved in with her and her husband and there was no real attempt to hide it. Admiral Nelson was kept at sea by angry naval bosses who wanted to frustrate his scandalous relationship with his mistress, a letter reveals.After being made Lord of the Admiralty in 1801, Sir Thomas Troubridge was said to have deliberately kept Nelson at sea for long periods so he could not be with his mistress, Lady Emma Hamilton, as their affair was a public scandal.Sir Thomas was once a friend of Nelson’s, but became his foe when he was promoted above the famously egotistical sailor. In a 216-year-old letter to Emma, Nelson wrote of his fury at Sir Thomas “lording it” over him and confessed to feeling seasick because he had been at sea for so long. Admiral Nelson writes in the letter that he feels sea sickCredit:IAA/BNPS Nelson found his treatment all the more galling as he had saved Sir Thomas from ridicule three years earlier at the Battle of the Nile where he ran his ship aground and was unable to take part.After leading the British to victory, Nelson insisted Sir Thomas still be given a gold medal commemorating the battle.But his feelings about his naval colleague had changed by October 1801.He wrote to Lady Hamilton: “Tomorrow week all is over no thanks to Sir Thos.”I believe the fault is all his, and he ought to have recollected that I got him the medal of the Nile. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.