I’m sure it happens to most biographers, but I must confess to an important error of interpretation in The Late Lord.
Mary, Countess of Chatham (ca 1800) by Charles Rosenburg of Bath; in the possession of Ron Mills
On pp. 181-2, I describe the death of Mary, Countess of Chatham, on 21 May 1821:
On Monday, 21 May 1821, Chatham, at home in Hill Street, received the visit of Sir William Bellingham [an old friend] … The two men sat down to dinner at 5 o’clock. Lady Chatham did not join them. She had been unwell with a liver complaint since Saturday … She greeted her husband’s guest, then took a glass of barley water and brandy laced with laudanum and retired early to bed. Her maid remained in the room with her as she drifted peacefully off. She was so peaceful, in fact, that it was some time before the maid realised Lady Chatham was no longer sleeping. … What exactly killed her is a mystery, although the signs point to an accidental laudanum overdose.
This passage came from two separate letters in private hands. I can’t reproduce either of them here, but one was written by J C Villiers, a close friend of Chatham’s who saw him on 22 May. The other was written by a third party, reporting a conversation with Sir William Bellingham.
I came across my transcripts of those two letters yesterday, and it immediately struck me that I had completely misinterpreted them. Eighteen months of not thinking too much about it allowed me to see new connections between the two accounts (which I had previously found somewhat contradictory).
Far from being a “mystery”, I think Mary’s death was due, not to any laudanum overdose in the barley water, but to the liver complaint from which she was suffering. It sounds like it was sudden but extremely virulent. According to Villiers’s letter, she was fine on the Friday and dead by the end of Monday. The crucial thing I’d missed is that Bellingham wasn’t there because he happened to be visiting: he had been called in because Lady Chatham’s death was imminently expected to happen, and Chatham didn’t want to be alone when it did.
Hyperacute liver failure it is, then. The only mystery is what might have caused Lady Chatham’s liver to fail so rapidly (under 72 hours).
The Late Lord 
A insight into how historians work. Pat-on-the-back stuff!
I only wish I’d noticed these things sooner
Top marks for coming clean on that but it is always disappointing to rethink after publication and to come to a different conclusion. I try not to and sleep better as a result….