A video explaining conception during sexual reproduction.
A healthy baby boy has been born in China four years after his parents died in a car crash.
The boy was born to a surrogate mother four years after biological parents Shen Jie and Liu Xi died.
The couple were in the process of trying in vitro fertilisation whenthey were killed in the crash.
They were scheduled to transplant one of the fertilised embryos into Liu just five days after the fatal accident in March 2013.
Both Shen and Liu's parents, the boy's grandparents, have spent the past four years fighting a legal battle to have the rights to their late children's embryos.
They finally won custody of the embryos last year and, since surrogacy is illegal in China, managed to drive to Laos and find a surrogate mother using an underground surrogacy agency.
The boy was born in December in a hospital in Guangzhou, China. His name is Tiantian, or "sweet".
"Tiantian's eyes look like my daughter's but overall, he looks more like his father," Liu's mother, Hu Xinxian, told Beijing News.
The grandparents have not decided how to tell Tiantian about his background. For now, they have decided to tell Tiantian his parents are overseas, until he's old enough to understand his background.
"This boy is destined to be sad on his arrival into the world. Other babies have their fathers and mothers, but he doesn't. We will definitely tell him in the future. How can we not?" grandfather Shen Xinan said.
