Toddler Oscar Dunkley received a life-saving heart transplant.
The 20-month-old from Bournemouth, Dorset, nearly died several times.
His very happy mother, Abbie Burkmar, said: "He is already a completely different child. We are very grateful to the donor family. "
The young man is no longer fed through a tube and is now learning what it is to explore the outside world.
Abbie said: "The new heart is working very well. He's a completely different child already.
Talking about the parents who donated her son's heart, she added, "Thank you, it's nothing close enough.
"They saved Oscar's life and changed all our lives.
"I hope they can find some comfort in what will be a horrible situation for them. It's still so early and I'm trying to deal with the emotions. Eventually, I think we're going to write to the donor family, but now they'll need your space.
"I think about them all the time – especially when we have a good day with Oscar, which we could not do when he did not leave the hospital. They must be going through so much …
"Oscar's quality of life is 100% better. Before, he was being fed through a tube and he would always be sick – now he eats proper meals.
"Even doing normal things, like taking him with us to the diner, he loves to see all the products. He loves to go out and gets so excited when he sees the car. "
Oscar was seriously ill with heart failure when his situation was highlighted on the front page of Mirror in November.
He could have spent days of death having survived for weeks before, when the powerful drugs that kept the organ almost failing.
Oscar had been in the hospital for months, when his parents received the news they craved. Abbie said, "At 4 o'clock in the morning, we got a phone call.
"Oscar was taken to Great Ormond Street Hospital by ambulance in an hour, so he was in surgery.
"It took about eight hours, so that day he had a new heart. We waited so long that everything happened so fast.
"We were in complete shock. He was sedated and had many wires in it, which was overwhelming. We were very excited. We had come so close to losing him so many times and I knew that another family had lost the child and been chosen to do it. "
Abbie, 24, believes that the successful Change the Law for the Life of the Mirror in Organ Donation campaign has helped her son gain his life savior gift.
She said: "I think it was a big factor for the Oscar to have its new heart."
After surgery, the little boy spent eight days on intensive care – but he is accustomed to fighting.
At four months of age, he was diagnosed with dilated cardiomyopathy – which means that parts of the heart are enlarged and the organ can not pump blood properly.
It's the same condition that affected Max Johnson, the 10-year-old boy who led the Mirror campaign.
Oscar's condition was administered until September last year when he was taken to the hospital with suspected bronchitis.
His parents then received the devastating news that he was having heart failure and his life was in serious danger.
Oscar, who has a four-year-old brother, Jack, lived in Southampton General Hospital and Great Ormond Street Hospital in London for five months with his father Josh and his mother Abbie taking turns at his bedside.
The parents supported our campaign, and the legislation, a private-party bill presented by Geoffrey Robinson of the Labor Party, got real approval in March.
This means that adults in England will be classified as having agreed to be organ donors unless they have given up.
It takes effect in 2020 and will be christened Max and Keira's Law in honor of Mirror Boy Max and Keira Ball, the girl whose heart is now pumping his chest.
Data from the NHS Blood and Transplant revealed to the Mirror that 23 people died waiting for a transplant within two months after it became law in March, and 868 patients were added to the waiting list.
Children who need a new heart usually expect two and a half times more than adults because mourning parents are less likely to agree with the organs being donated. Last year, 426 patients died while on the waiting list – 17 were children.
Donors and their relatives are anonymous but, through health authorities, Oscar's parents can contact their donor family if they agree.
Abbie said: "I hope that in a year we can write to them and tell you how well the Oscar is."