Natalie Bassingthwaighte breaks down and struggles to breathe after learning the truth about her grandmother on Who Do You Think You Are?

Natalie Bassingthwaighte couldn't contain her emotions after making a shocking discovery about her grandmother on Tuesday's episode of Who Do You Think You Are?

The 45-year-old performer travelled to Peelwood, a country town in NSW, where her maternal grandmother, Gwen, was raised.

'I had heard a story that my grandma's mum wasn't her mum. It was brushed over and it wasn't really talked about, and I don't really know anything outside of that,' she admitted.

Sitting down with a genealogist, Natalie was shown her grandmother's birth certificate, where she discovered Gwen's mother's name was Florence, and the father was not listed.

The genealogist explained that Florence had given birth to Gwen out of wedlock when she was 22 years old.

'The beliefs back then were if a woman had a child out of wedlock, she either married the father or the baby was adopted,' explained the genealogist. 

'But Walter and Catherine, Gwen's grandfather and grandmother, decided to go against the Catholic Church and raise Gwen as their own.'

They did this as a way to keep the baby within the family, with Gwen growing up thinking Florence was one of her sisters.

After discovering her grandmother never got the opportunity to talk about what had transpired with her biological mother, Natalie broke down in hysterical tears.

'Oh, I can't breathe,' she sobbed, while doubled over, gasping for air.

Natalie later admitted she was surprised by her dramatic reaction to the news about her grandmother's upbringing. 

'I'm trying to process why I'm feeling so upset. Um... I had a child out of wedlock, so when you put your current life into context, it's very strange,' she reflected.  

'Giving up a child would be really horrific. I just think you would feel so sad. I can't even comprehend that the mother wouldn't say anything or just like, yearn to cuddle her, or to be the mother, not the sister. 

'I remember Grandma being quite stoic. There was a presence about her that kind of makes sense now, hearing some of that.'

Natalie is a mum to daughter Harper, 10, and son Hendrix, eight, who she shares with her husband of 10 years, drummer Cameron McGlinchey.