Sophie Levett, 26, and her eight-year-old son Callum, from Selsey, were overtaking an articulated lorry on the A27 when a tyre blew.
It careered them straight into the lorry and then a wall at speed, flipping and crushing their Peugeot 206.
Chris Levett said the male lorry driver and another female driver pulled grandson Callum out of the vehicle with only cuts and bruises, while another man comforted Sophie, who suffered a broken shin bone and is left ‘battered and bruised’.
Sophie was 24-weeks pregnant and tragically her unborn baby didn’t survive the accident, Chris said.
Chris said Sophie lost consciousness and when she came to, upside down, and couldn’t see her son in the mangled vehicle so panicked, thinking he was dead.
The incident happened around 2.35pm on Wednesday, December 3 and shut the A27 for hours between the Fontwell and Tangmere roundabouts.
Chris, 47, said: “A police officer rang last night (Thursday) and explained that they believe her tyre blew as her car was overtaking it.
“Thank god for the metal bars on the back of lorries because they would have gone under it otherwise and it would be a very different story.
“Sophie lost consciousness and when she came round she was petrified what had happened to Callum.
“The lady driving behind, who saw what happened, pulled Callum out with the lorry driver, and put him in the cab to keep him warm.
“A man police haven’t yet identified stayed with Sophie in the car and comforted her.
“She was convinced they were lying when he said he was OK, she was convinced he was dead.”
Callum escaped with small grazes on his chin, forehead and back, small cuts on his head and a bruised thigh.
Mum Sophie underwent an operation at St Richard’s Hospital in Chichester on Friday to put a metal pin in her broken shin and has had glass removed from her cheek.
Chris said she has been left ‘battered and bruised’ and had lost the baby she was carrying.
He said: “She was 24-weeks pregnant and knew straight away because as soon as she got to hospital they did a scan which showed their was no heartbeat.
“You can understand how it happened with an accident like that, it’s devastating news for her.
“They didn’t know the sex and didn’t want to until the birth.
“She had a miscarriage at 22 weeks earlier this year so it’s doubly devastating for her.
“Her finance Daniel Lund has been by her side in hospital since it happened, it’s something I’m extremely grateful to him for.”
Chris said Daniel phoned him around 5pm on Wednesday to say there had been a crash, that Callum was OK but that Sophie was ‘critical’.
“I rang Sophie’s mum and we both dashed down to Chichester straight away,” he said.
“Many years ago my mum was in a similar accident, it was amazing she made it out alive but she was left in a wheelchair.
“So this brought it all back and my mum was terrified she would be left in the same situation, so it was beyond a relief when we heard she was OK as well.”
Chris, from Lancing, said Sophie grew up in the Worthing area and she went to Durrington High School before moving to Selsey with Daniel and Callum.
The A27 was closed for hours as the vehicles were recovered and the road was cleared of debris and diesel.
Chris said he and Sophie’s mum, Sandra Dore, were grateful for the help of those present at the time and to the emergency services.