The couple recently welcomed daughter Colette 'Coco' Josephine Williams via surrogacy after a ''long and difficult'' struggle to have another baby and everyone they work with on 'The X Factor' was shocked when they announced the exciting news.
A show source told The Sun: ''It took everyone by surprise. Nobody could quite believe it. Even Simon Cowell didn't know.
''We've seen lots of Robbie and Ayda lately. They have been on great form on the judging panel. The fact they were going through so much behind the scenes has come absolutely out of nowhere.
''But obviously everybody here is delighted for them and we look forward to seeing them again at the next stage of filming.''
Ayda announced the new arrival on Instagram, sharing a picture of their hands and those of their children, Coco, Theodora, five, and Charlton, three.
Ayda wrote: ''I spy with my little eye an extra little hand ... So we have been keeping a very special secret! We are delighted to share with you that we have had a baby girl....welcome to the world Colette (Coco) Josephine Williams!!
''It has been a very long and difficult path to get here, which is why we have kept it on the down low. Family comes in all forms, and this little lady, who is biologically ours, was carried by an incredible surrogate mother, to whom we will be eternally grateful. We are over the moon to have this beautiful baby girl in our lives and so blessed that we live in a world which makes this possible. As with Teddy and Charlie, we ask that you respect Coco's privacy and allow us to grow into our new team of 5! #TeamWilliams (sic).''
Robbie and Ayda joined the 'X Factor' panel this year, alongside Louis Tomlinson and Simon.