Klass, who is in a relationship with PR boss Simon Motson, has two daughters, Ava, 11, and seven-year-old Hero, from her previous marriage to Graham Quinn.
Her famous friends congratulated her, with Spice Girl Emma Bunton commenting on Instagram: “Such wonderful news! So happy for you all.”
Presenter Kirsty Gallacher wrote: “Oh how wonderful, congratulations to you all.”
Britain’s Got Talent judge Alesha Dixon wrote “congratulations darling”, and former Geordie Shore star Vicky Pattison said the news made her “so unbelievably happy”.
Earlier this week, the former Hear’Say star was announced to be returning to host the Global Awards on March 7 for the second year in a row alongside Rochelle Humes and Roman Kemp.
