The 24-year-old vlogger was pregnant with her son, and was only a few weeks away from her due date.
The cause of death has not been confirmed.
In an Instagram post, Thea’s mother revealed the YouTube star and her partner, Global Boga, had named their baby Reign.
She wrote: “To all Nicole’s friends and supporters it is with great sadness that I have to inform you that Nicole and her son she and Boga named Reign sadly passed away on Saturday morning.
“Also Nicole pre-scheduled a few YouTube videos and Boga has made the decision to allow them to be aired.
“As a family we ask that you give us privacy because our hearts are truly broken and we are struggling to cope with what has happened. Thank you her mum.”
Thea’s mother added: “RIP My beautiful baby girl Nicnac and my grandson Reign, I will miss you for the rest of my life until we meet again in eternal heaven.”
The star had more than 85,000 subscribers on YouTube, where she posted videos about her life and pregnancy, as well as hair tutorials and travel and dance videos.
Many fans paid tribute to Thea and Reign with messages on Twitter.