Billie joked that her rounded tum has spouted from nowhere, while posing in just her underwear for a mirror selfie.
She told her followers: "Wow baby bump where have u come from ... #halfwaythere #20weeks #excited #happysunday #babybump."
Billie is expecting her second child with fiance Greg Shepherd. They are already parents to daughter Nelly, two.
The reality star first announced news she is pregnant again in September. While on holiday, Billie shared a photo of herself, Greg and Nelly to Instagram, with Nelly pointing at Billie's stomach.
Alongside it, she revealed: "...And then there were four."
Billie's sister Sam Faiers, meanwhile, shared her excitement at becoming an auntie again and told her fans: "I am so excited to become an auntie again. Baby no2 #blessed @billiefaiersofficial @gregory_shep."
She also claimed that Billie is hoping for a baby boy this time round, just like her son Paul who was born in December last year. Sam told Reveal: "She always says she wants a Baby Paul, but I've always imagined Billie with girls."
Billie's pregnancy came just weeks after she announced her exit from The Only Way Is Essex. Billie had decided to quit the ITVBe reality show to focus on her family.
She told us: "I just think my time is kind of done there."
When asked what was next for her, Billie revealed that she had been trying to fall pregnant again. She added: "I am trying because I would like to have another baby soon. Obviously you can't exactly schedule it. It happened really quickly with Nelly, so I'm just going with the flow."
Billie first joined TOWIE, alongside sister Sam, in 2010 when the show first aired. She went on to star in eighteen series, before fans saw her bow out of TOWIE onscreen in August.
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