Helen and Arun Kumar had planned to marry in September at the Grade II-listed Law Society in Chancery Lane, London.
But after learning their daughter Elsie’s leukaemia had returned they married a few weeks ago in the capital’s Great Ormond Street Hospital instead.
Mr Kumar, 41, said: “She was on great form, despite being on five days of strong chemotherapy just before. She stole the show."
The father said they had already booked the venue, sampled the food and bought the wedding dress.
He continued: "The plans went on hold when we suspected Elsie had relapsed as we didn’t want to do anything without being certain what our future held.
"When doctors confirmed that she had, we decided to move the wedding forward. We wanted to get married with her there.
"It was a fantastic day. All our family and friends came, and Elsie was the flower girl, going up the aisle behind Helen on her trike.
"She was on great form, despite being on five days of strong chemotherapy just before. She stole the show.”
Elsie is one of the one in 10 children with Down’s syndrome that also has transient abnormal myelopoiesis (TAM), a leukaemia-like condition that initially resolves itself without treatment.
Children with TAM have a one in five chance of developing myeloid leukaemia around the age of two.
For months, there was no sign of the disease in Elsie. Then, last summer, Mr and Mrs Kumar, of Islington, London noticed their daughter’s lethargy and lack of appetite.
When a bruise appeared on her head in October, despite the fact she had not fallen or knocked herself, they decided to take her to the Whittingdon Hospital in North London.
She was referred to Great Ormond Street, where medics confirmed 10% of her blood cells were leukemic.
"Doctors don’t tend to treat until the leukemic cells reach 20% as there is a slight chance they could go away by themselves," said Mr Kumar.
"We monitored her but, within a month, the level of leukemic cells grew to 50%, so in November, Elsie started chemotherapy."
Elsie’s future looked hopeful when she went into remission in December.
Throughout January, February and March, she underwent three further rounds of chemotherapy to minimise the risk of a recurrence.
"The little girl we knew before slowly started to come back. After being stuck in the same place for so long, she started coming on leaps and bound," Kumar added.
But by May, her appetite began to wane once again.
"We had to coax her more and more to eat, but her blood counts were fine, so we thought it might just be the terrible two’s, or chemotherapy changing her taste buds," said Mr Kumar.
In June, alarm bells rang once again when a single blood spot appeared on Elsie’s skin.
Worried, Mr and Mrs Kumar took her back to the Whittingdon, where a consultant broke the heartbreaking news that the cancer had returned.
The couple then faced an impossible choice – whether to opt for palliative care and take Elsie home to enjoy their remaining time together or to risk the side-effects of another, stronger round of chemotherapy.
Mr Kumar said: "Although the side effects of chemotherapy can be horrendous for children with Down’s syndrome, Elsie hadn’t experienced them before.
"Our consultant agreed that she was strong and could handle it, so we decided to give her the chance to fight."
Now, the family have been told a blood stem cell transplant is the best chance of a cure and have issued a desperate plea for donors.
Because Elsie has no siblings and is of mixed heritage – Indian and white British – the chances of finding a match are reduced.
According to Delete Blood Cancer, only 60% of white people in the UK can find the best possible stem cell match from a stranger.
The statistic drops dramatically to just 20.5% for patients from a black, Asian or ethic minority background.
The Kumars are sharing their story in the hope that they will encourage more mixed race people to register as donors.
They have launched an online donor search, setting up Facebook and Twitter accounts called A Match for Elsie.
Save for a few exclusions, including those who suffer from chronic illnesses, any healthy adult living in the UK and aged between 18 and 55 can register to be a donor.
Pre-registration is possible from the age of 17.
Praising his daughter’s attitude throughout her battle, Mr Kumar said: “Elsie is incredibly brave.
"She doesn’t want to be ill, she just wants to play and be a normal toddler. We take her out every morning so she can play on the swings for half an hour or so before returning to hospital.
"We’re urging people out there to sign up as donors because they could save a life."
To help Elsie, visit http://www.deletebloodcancer.org.uk/en/a-match-for-elsie.