Thai police say Danny will be charged with causing death by reckless driving, the BBC reports. The truck driver Natt Awut Timsu will also face the same charges.
Sophie became famous for campaigning for mothers to continue to breastfeed their children until age eight, and her YouTube videos documenting her with her 4-year-old son, Shaye. She was pregnant with her second child to Danny.
Her partner confirmed the news on Facebook overnight, writing, "Tragic news my girlfriend died in a scooter accident we had today."
"I am in total shock as I've lost the most precious person I had ever connected with.. my brain keeps going into denial. I am distraught. She was also pregnant so I lost my child too."
"I do not have access to all of her friends or family members so if you know any of them please notify them that this has happened."
"I need as much love and support as I can get from everyone," he finished.
Sophie's YouTube channel 'Sophie's Joy Breastfeeding Mama' had amassed more than eight million views, with one video of her breastfeeding Shaye viewed over 25m times.
A police officer at the scene said, "She was riding on a motorbike with her partner when they changed lanes to avoid a vehicle parked and blocking their path in the motorbike lane of the road. As they did this, the truck hit them from behind. The woman was then run over by the truck and sustained fatal head injuries," reports the Daily Mail.
It's believed the driver of the truck has handed himself into police after initially fleeing the scene.