For most of his life, he has been battling a killer condition, from which his parents feared he might never recover.

Now, after three-and-a-half years of chemotherapy, the little star has finally been told he is cancer-free.

Jubilant parents Donna Cox and Lee Stewart say they cannot believe their son is on the road to recovery.

Not only has Sam, of Houghton, been forced to fight leukaemia, he was also born with a hole in his heart and a genetic condition so rare that it has baffled experts at Newcastle's Centre for Life.

Donna, 32, said: "They have just tested his bone marrow and finally told us it is completely healthy. No one can believe it.

"We've been having a party to celebrate."

During his young life, Sam has undergone more tests, operations and visits to hospital than most people ever do.

He was born at Sunderland Royal Hospital weighing a healthy 6lb on August 4, 2003. Just six hours later, doctors picked up a murmur, which tests revealed to be a hole in the left chamber of his heart.

Transferred to the Children's Heart Unit at Newcastle's Freeman Hospital, he underwent open-heart surgery at just four months old.

It was while tests were being carried out that doctors also discovered Sam, who has a brother, Nathan, eight, was suffering from a rare chromosome disorder.

Donna, a medical receptionist, said: "Sam's condition is known as a mosaic disorder and affects his development.

"It is very rare. In fact there is not another family in the world with exactly the same condition. It means Sam's speech is delayed but, luckily, we have managed to get him into a mainstream nursery in Houghton."

Just as the family were coming to terms with the youngster's heart and chromosome problems, they were suddenly hit by another bombshell.

On January 2, 2005, after discovering a pin-like rash on their son's hands, Donna and Lee, 34, an account manager, were told Sam had leukaemia.

Donna added: "At first, they thought it was meningitis, but the blood tests came back and showed something different.

"It was horrendous. I just remember Lee and I both shouting 'no' at the same time. We really thought he was going to die."

Between January and August, the family spent most of their time at Sam's bedside on Ward 11 at Newcastle's Royal Victoria Infirmary.

During the first year of treatment, Sam underwent intense bouts of chemotherapy which left him exhausted.

Today, things are looking very different. Final tests show Sam is now cancer-free.

Donna added: "He has so much energy now, it's incredible. I think he understands everything that's happened, even though he can't really say it."

The family have to return to the Centre for Life every year, as experts continue to assess Sam's other condition.

"We're just looking forward to things getting back to normal – whatever that is," added Donna.