The loved up couple - who tied the knot in Rome back in 2012 - revealed the happy news on Thursday (22.06.18) and said their two-year-old son Milo is already ''the perfect'' older sibling.
In a statement to PEOPLE magazine, they confirmed the new arrival and added: ''We are over the moon with happiness and Milo is the perfect big brother.''
The 'So You Think You Can Dance' host had previously opened up on how excited she and her partner were to find out they were going to become parents for the second time.
Announcing her pregnancy in January, she tweeted: ''Over-the-moon to share that Milo is going to be a big brother! Can't wait to be a family of four in the spring. We're all so excited.''
Meanwhile, Cat, 41, admitted in March that they were still yet to choose a name for their baby, and she was planning to ''wing'' the tough decision because she doesn't want it to cause an argument between her and her husband.
Speaking to Entertainment Tonight, she said: ''We never agree on names, my husband and I, so we're just going to wing it! I think I will always win at the end of the day, because I've done all the hard work. So I'm just not going to say anything. Let's not argue about it right now. I'll just win when it comes up, right?''
And the blonde beauty was enjoying her pregnancy but admitted she had to ''constantly'' go to the bathroom and was always craving her favourite snacks.
She joked: ''I'm feeling pretty good, apart from the fact I need to pee constantly. I'm like, 'OK, where is my nearest Starbucks or Whole Foods?''
Ahead of their upcoming tour, and prior to the release of their long awaited album, Smoke Fairies played a great warm-up gig at Elsewhere in Margate.