I was completely unprepared for the way it hit me yesterday - the sheer force of heart-break emotions as, there in front of me, stood 'what might have been' or, rather, 'what SHOULD have been' if it wasn't for the way the eating disorder had stolen such a massive chunk from Ben's teenage life.
It was Founders Day at school; the bi-centenary service. And, because of my former role in the PTA, I'd been invited to attend.
Along the route from the car park, snaking through the school grounds, stood pairs of Prefects, all smartly dressed in their school 'colours', guiding alumni, governors - and me - all the way to the gothic school chapel.
Each one of these Prefects was from Ben's social group - the young people that had been his bosom pals throughout the first four years of high school and, if it hadn't been for the way the ED robs its victim of their social life and skills, who would still be his bosom pals.
But this wasn't what hit me like a violent bolt of lightening.
It was the fact that ALL of them were there. All of them, except Ben.
And they all looked healthy, happy, mature and confident - just like 18 year old senior school pupils should look.
Their school careers had gone from strength to strength, culminating in the role of Prefects in the school's most important year since its centenary in 1912.
They were the epitome of what I had dreamed for Ben when he won an academic scholarship to that wonderful school, all those years ago. A school that had produced, amongst its current alumni, CEOs of top corporations, law lords, heads of the armed forces and so on.
Mind you, I'd never dreamed of Ben becoming General Sir Thingumy Whatsit or The Lord X of Y.
All I'd wanted for him was a happy, supportive place in which to study - a school known for its ability to nurture pupils to achieve their full potential, not just academically but personally, too.
And that had happened. For the first four years, at least. Ben was happy, confident, sporty and academically bright, one of the most popular boys in his friendship group and a rising star on the Rugby field.
Physically, he was transforming from a boy who'd carried a bit of 'puppy fat' into a handsome, athletic young man. I was so proud of him that it hurt.
So here, lining the route from the car park to the school chapel, were all Ben's friends.One after the other, all the way into the chapel, culminating with the Head Boy - the boy who had been Ben's academic, sporting and social rival yet close friend through those first four fulfilling years at the school, a boy who could have been his school 'twin' in almost every way, even physically.
But not now.
Here was what Ben could have been, what he SHOULD have been, but wasn't, thanks to the ED.
Over six foot tall, athletic, confident and mature.
One by one I acknowledged Ben's friends in that long line up to the chapel, my heart breaking in a way I hadn't predicted.
Ben should have been there with his friends, looking like his friends, behaving like his friends. And I should have been making my way to the chapel as proud as proud can be about the way the school had nurtured my son into 'one of the class of 2012'.
Instead my heart was breaking at the way the eating disorder had stolen a promising school career from him. The way it had robbed him of his friends and social life. The way it had stunted his growth and physical development. The way it had completely transformed his life, and ours.
I wish I'd stayed at home.