Speculation began earlier this month that the 'Smile' singer is expecting another baby with husband Sam Cooper in December.
The singer also referenced the reports of her pregnancy earlier this month by tweeting: "Thank you for all your congratulations today. I honestly couldn't be happier. such an honour to be on the list! #Timestop50tweeters."
During an appearance on This Morning today (July 16), Keith finally confirmed the news on her behalf, saying: "Yes, she is pregnant."
Allen and Cooper are already parents to a daughter named Ethel Mary, born last November.
Allen announced that she was to become a mother for the first time at the couple's wedding reception in June 2011. The 27-year-old previously suffered two tragic miscarriages.
The 'Not Fair' star has also hit the headlines recently after reporting a member of the British Army to the Ministry of Defence over a perceived racist tweet.
The furore - which apparently stemmed from Allen misinterpreting the tweet - was resolved after she received flowers and a handwritten apology from the man in question, Harry Wilson.