The 28-year-old shared the surprise news at the Uber x Red Cross Farewell Fashion Show in Sydney, much to the shock of her husband-to-be, Sam.
"Here's a note to everyone, if you buy a pregnancy test, maybe you should let your partner know you've done that," he joked.
The pair met while filming the first season of Bachelor In Paradise in Fiji. Sam proposed to Tara in the series finale and the loved-up couple currently live together in the Gold Coast.
Earlier this year, the pair opened up to WHO magazine about their plans to start a family one day.
"Tara is a professional nanny," he says, "but I have grown up with babies around me all the time, and toddlers, because my siblings keep breeding! We are both so in tune with kids - so absolutely. She is going to be a beautiful mum."
This article originally appeared on WHO.