He was talking about their disabled son, Ivan, who tragically died at the age of six.
In his speech to the Conservative party conference, the Prime Minister reflected on how he felt when pushing his son in his wheelchair.
His voice cracked as he revealed his hope that society's attitude to disability had changed since the Paralympics.
As he spoke, Mrs Cameron was seen welling up in the audience in Birmingham's Symphony Hall.
The PM said: "I am so grateful for what all those Paralympians did.
"When I used to push my son Ivan around in his wheelchair, I always thought that some people saw the wheelchair, not the boy.
"I think today more people would see the boy and not the wheelchair – and that's because of what happened here this summer."
TV cameras caught Mrs Cameron sitting in the auditorium with tears in her eyes.
Ivan, who had cerebral palsy and epilepsy, died aged six in 2009. The couple have three other children Nancy, Arthur and Florence, who was conceived after Ivan's death.
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