A hospital nurse broke down in tears as she told an inquest of the moment she handed a patient a cup of Flash floor cleaner mistaken for water.
Staff nurse, Alba Duran described her "normal" shift in the Baily ward, which began at 7.45pm, before something "really strange" happened after she gave Mrs Blaber her medication at around 10pm.
Hours after, Joan Blaber was "frothing at the mouth" and "fighting for her breath" before dying six days later, the hearing on Thursday was told.
Flash was not even a "necessary" cleaning product for the hospital to stock and was merely used to make the building smell clean, it also emerged during the hearing.
Described as a "chatty, lovely lady", Mrs Blaber was admitted with a minor stroke on August 22 but her condition worsened after the incident on September 17 and she died on September 23.
The pensioner was given a mixture of medication and pain killers on an empty stomach because a sore mouth had put her off her meal, the inquest heard.
The young Spanish nurse told the inquest how she poured pink summer fruits squash into a beaker from a bottle on Mrs Blaber’s table and then added what she thought was water from a green water jug.
Although bedside lights were not on, she said there was "enough light to see" in the ward.
She said: "I gave her the beaker. She took her medication."
Around 15 minutes later Mrs Blaber started coughing, vomited twice and was "very sleepy".
Growing tearful, Ms Duran said: "(My colleague) went to give her some water from the jug. She noticed that the liquid in the jug was not water, it was something else.
"I went to see what happened. I took the jug with me to see myself what it was. I poured the liquid from the jug and I could see it was a yellow/green. I put some of it on my gloves and rubbed my hands and could notice there were bubbles on my gloves.
"It smelt of lemon and reminded me of something (that might be used for) cleaning."
She began searching the ward for products it could be and discovered a five-litre container of Flash in an open cupboard behind a trolley just metres from the bedside.
Ms Duran said: "I grabbed it. I thought this might be the same because it was the same colour."
According to hospital protocol, the Flash should have been locked inside a nearby storage room with other chemicals. On the day of the incident the store was left unlocked, the inquest has previously heard.
A doctor was called and the National Poisons Information Service consulted. Ms Duran sat with Mrs Blaber through the night and she was stable. But at around 7am the next morning she began to deteriorate and was moved to the high dependency unit.
Ms Duran added: "I was very nervous after that happened."
As she left the witness box Ms Duran burst into tears and Mrs Blaber’s relatives reached out to take her hand as she passed them.
Healthcare assistant Linda Stephens said in a statement a staff member told her that "Joan was frothing at the mouth that morning (the next day) and fighting for her breath."
Mrs Blaber’s clear water jug had been removed in the afternoon and was replaced with a solid green jug when returned, meaning no-one could see the liquid inside, the inquest heard.
The hospital’s system of using different types of water jugs to identify the needs of patients was a "complete red herring" because it was "abundantly clear that no-one had any idea about the system of the jugs", senior coroner Veronica Hamilton-Deeley said.
Barbara Kavanagh, a hospital training manager, also told the inquest Flash was not a "necessary product" because microfibre mops and cloths were used.
She said Flash was used to "enhance the confidence (of people) in the place being clean" because of the "scent", adding: “We don’t need it to clean.”
The inquest, taking place at the Jury’s Inn hotel near Brighton Station, continues on Friday.