Connie Yates and Chris Gard spoke out in solidarity with the parents of terminally ill toddler Alfie Evans, who died on Saturday morning, and said it is "impossible" for others to "understand their pain".
In a statement, the couple said: "With heavy hearts we have watched as Alfie's case has unfolded. For those who have not been in a situation like this, it is impossible to understand the pain Tom and Kate are going through.
"When we were fighting for our son, Charlie, to be given a chance to try a treatment that could have improved his quality of life, we realised that cases like these would keep happening until the law was changed.
"Tragically, this has proven to be true."
Charlie died in July last year after he was diagnosed with a rare genetic disease.
Both Charlie and Alfie died after their life support was switched off following rejected legal bids to transfer them to the US and a Vatican hospital, respectively.
In both cases, UK courts agreed with the youngster's doctors that keeping them on life support was not in best interests.
Charlie's parents are fighting to have new legislation introduced called Charlie's Law, which they have said will help "prevent parents experiencing painful and prolonged conflicts with medical professionals".
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