The mum announced the news and revealed her choice of baby name on Instagram with a photo of her baby's tiny hands.
"Welcome to the world baby girl 💗 Siera Aleira Horsley," she captioned the post.
"Born at 11.13am this morning- weighing 7lbs 1 💗
"She's perfect 😍"
Thomas had packed her hospital bag just 23 hours earlier, sharing a picture of her essentials (and a last min trip to the hair dressers) on Instagram.
She captioned the image: "Ready to meet baby no2 👶🏼 hospital bag ready! 💗 roll on....💛"
She certainly didn't have long to wait!
The relaxed mum-to-be also shared a bedtime selfie the night before her second daughter's arrival.
Thomas and her boyfriend Adam Horsley also have a two-year-old daughter called Ariana.
Congratulations Imogen and Adam!