David Cameron has spoken of his grief at the death of his son in a letter to the parents of a brain tumour victim.
The Prime Minister said he missed Ivan, who had cerebral palsy, every day - but could now sometimes feel happy thinking about him.
The insight came in a hand-written reply to Paula and David Holmes after they urged him to put more money into researching the cause of brain tumours.
The couple, whose 10-year-old daughter Katy died from the illness, appealed for him to consider the issue with his "dad head" on.
According to the Lancashire Evening Post, Mr Cameron's response to their letter said he knew from losing his six-year-old son in 2009 that the pain "never truly goes away".
"I am so sorry to hear of your loss," he wrote. "I miss my Ive every day, but at least I do sometimes now feel happy and not sad when I think of him.
"The point that you make about causes and medicines is a really powerful one.
"I will check myself that the research programmes are properly directed."
The missive was signed: "With love and best wishes David Cameron (with my dad head firmly on!)."
Mrs Holmes told the newspaper: "We are over the moon at getting this reply from David Cameron. We asked him to show us that he cared and by hand-writing this letter, he has done exactly that."