HER newborn baby was sleeping soundly beside her in his hospital cot as Caroline White stared at him, still bleary-eyed with the exhaustion of giving birth, but savouring the joy of new motherhood.
It was the middle of the night and she couldn't sleep, despite her fatigue.
So she picked up from the bedside table her son's Personal Child Health Record - an official log in which doctors and nurses write notes about a newborn baby's progress.
"A sixth sense must have told me things weren't quite right with the way hospital staff were acting," says Caroline.
"A paediatrician had told us he thought Seb might have a chromosome disorder, but he didn't go into detail. In Seb's notes they'd written things such as 'floppiness' and 'upward slanting eyes' — characteristics I knew were typical of babies with Down's syndrome."
Feeling a mounting sense of panic, Caroline went on to a computer for the use of patients beside her bed and Googled "Down's syndrome".
"I looked across at my son and suddenly all I could see was Down's. At that moment, the bottom dropped out of my world and I felt totally cheated. It was the worst moment of my life," she says.
"It sounds selfish and naive, but all I could think was: 'This shouldn't have happened to me'."
She was in tears when she rang her husband, Simon, at home. There had been no official diagnosis, but the clues that something was seriously wrong were all there.
"I was in shock," says Caroline. "I remember Simon was totally calm, saying that whatever the problem was, we'd deal with it, but I was so frightened and upset I couldn't see how I would ever deal with it.
"The woman in the bed opposite me had been warned that she was at high risk of having a Down's baby because she was 42, but her little boy was perfect.
"I was only in my 30s and it seemed as if my little boy wasn't perfect, which struck me as so unfair."
That was four years ago. Today, Seb White is an irrepressible little boy — and an unlikely new TV star.
He appears in Marks & Spencer's Christmas TV advertisement, which aired for the first time last Wednesday.
Dressed in a cardigan and bow tie, his eyes sparkling with joy, Seb steals the show.
At the home he shares in Bath with his two-year-old brother, Dominic, and parents, Caroline, 39, and Simon, 36, Seb is as winning in the flesh as he is on TV.
After greeting me with a handshake, Seb pulls me over to the TV. As Caroline puts in a DVD of the 50-second TV advertisement to show me, Seb jumps up and down before high-fiving me.
"Look, look. It's Sebi!" he says.
Seb's adventure began in July when his mother posted a message on the Marks & Spencer Facebook page, asking why her little boy couldn't be considered for their ad campaign just because he has Down's.
The company responded, auditioned Seb, then cast him in their festive catalogue, which is out this week, and in their iconic Christmas TV advertising campaign.
"We can't quite believe what's happened,' says Caroline, a part-time retail product manager.
"Seb isn't in the advert as a token, he's there because he's gorgeous — a mischievous, lovable little boy who happens to have Down's syndrome.
"If Seb appearing in a TV campaign raises awareness of Down's, challenges stereotypes and helps other parents feel better about having a child with it, I will be very happy."
The truth is that until Seb was born, Caroline lived in virtual ignorance of Down's: when she was pregnant, she ignored any mention of it because she didn't think it could be relevant to her.
So when her son was diagnosed, she thought her life was over.
"If I'd known in advance that I was going to have a Down's baby, I would quite possibly have had a termination," she says.
"Now I see his beauty and personality shining so brightly, and hope that the more people see Seb, the more I can change people's negative perceptions of Down's."
Life had seemed perfect when Caroline became pregnant with Seb within months of marrying Simon in March 2007. They'd met through friends, married after three years and couldn't have been more thrilled to be expecting a baby.
When Dominic was born in September 2010 — without Down's syndrome — Caroline admits it was a bitter-sweet moment.
"I was ecstatic, but I also felt guilty," says Caroline. "I knew I should have felt the same joy when Seb was born, but I'd been so fearful and so ignorant then."
As Seb hit every milestone - albeit slowly — Caroline began to relax about the future.
Seb grew into a happy, delightful little boy. "He is incredibly sociable and very empathetic," says Caroline. "He's the first to notice if Dominic is upset and will rush over and cuddle him.
"It's the same with everyone in the family — he instinctively knows when anyone needs a hug."
In July, with Seb preparing to start primary school, the family went to Marks & Spencer to buy his uniform.
Having looked through the store's Back To School brochure and at the in-store posters of children starting school, Caroline realised that none of them looked like Seb.
"I didn't feel like any of this was meant for my little boy and that really hurt," she says.
So Caroline took decisive action. She posted a photo of Seb on the Marks & Spencer Facebook page, asking if the company would include him in their modelling campaigns.
She wrote: "He has striking, unusual features, charms the pants off everyone he meets and his little face is full of magic and mischief. He also has Down's syndrome.
"When he was born, I was shocked to my core.
"I knew nothing about the condition, and what should have been the happiest day of my life was the worst.
"My heartfelt desire is to get the message across that 'different' isn't any less wonderful or even that different."