Holly Hatfield, 23, had been looking forward to travelling home from Berlin to East Midlands Airport last July after completing her studies for her masters degree in the German city.
But she was mortified when she went to take her seat and discovered that she had to move due to her size - and would need a seatbelt extender.
Holly weighed 23st 7lb at the time and was a size 28.
Holly Hatfield, 23, from Belper in Derbyshire lost an incredible 12 stone in nine months
'I had always been big, but the incident on the EasyJet flight was the catalyst for finally taking action to lose the weight,' said Holly, from Belper in Derbyshire.
'I boarded the busy plane and managed to grab an aisle seat - a seat I normally chose on account of the extra space.
'I realised at that moment that I would need a seat belt extender, but when I asked for one the flight attendant explained that because I was the last row they could not have any one using an extender in those seats.
'She then asked a lady in the row in front of me if she would swap seats. The passenger had a spare seat next to her.
'The airline handled the move discreetly and without fuss. But a school group who had been sat opposite had witnessed the whole thing - it was a pretty painful and mortifying experience.'
Holly pictured on her graduation day at Keele University. She slimmed down from 23st 7lbs to a svelte 11st 7lbs
She turned a blind eye to the warning signs that her weight was spiralling out of control, even when she used to call her dad from the bottom of the road leading to their family home asking for a lift up the hill.
But the plane ordeal persuaded her to tackle her weight once she arrived back in the UK.
'I'd always been on the big side,' she said, 'even at primary school I was always the biggest of my friends and I got bigger in high school.
'As I got older and had my own money to spend I would treat myself to a lot of fast food after my lessons.
Holly - pictured at the start of her weight-loss journey, was mortified to need seatbelt extender on flight
'And when I got to university I continued to eat a lot of take always and didn't take time to cook healthy meals. Instead I relied on convenience food.
'I ate a lot of carbs. My meals were often all about the bread. I was definitely a boredom eater.
'When I was at a loose end I would look for something to eat to occupy my mind.
'Holly embarked on the LighterLife weight management programme from August 2012 until April, took yoga classes ans went swimming. She also saw a counsellor who coached her into cutting down on carbs''I wasn't an emotional eater, I've never been bullied and I never had family issues.
'If I was at home and there was something in the kitchen I would pick it up and graze on it without giving it a second thought.'
As her weight continued to rise, Holly, who attended Keele University where she also studied for her first degree in sociology and American studies, turned a blind eye to the negative impact it was having on her life.
'It just seemed like I would never be able to stop eating or slim down, so it became easier not to do anything about it,' she said.
'It did hold me back though. I realise that now. I wasn't able to do any of the activities that my friends were enjoying. If someone was going on a bike ride, I couldn't go. PE was always a nightmare.
'There are lot of hills in Belper where I live. I found it very tiring to walk anywhere, so it became easier just to stay at home.
'I used to call my dad to ask him to pick me up from the bottom of our road in his car and drive me home.
Holly, pictured with her father Ray in 2012, embarked on a LighterLife programme and started exercising
Holly pictured at the Olympic Park in 2012. She slimmed an incredible eight dress sizes after the plane incident
The retail assistant had tried various diets before but they had done nothing to curb her obesity.
Then she tried the LighterLife weight management programme and started the diet in August 2012.
She was provided with specially formulated food packs, including soups, porridge, milk shakes and snack bars which she used for eight months until April.
She also attended counselling sessions, in which she was coached into cutting down on the carbs and instead eating more fresh fruit and vegetables. And she began exercising, taking swimming and yoga classes.