Adam, who plays Adam Barton in ITV soap Emmerdale, and his wife confirmed the happy news to OK! magazine, revealing that the baby was conceived on their wedding day.
The couple, who tied the knot earlier this year, are already parents to son Teddy, whom they welcomed in 2014.
'I'd been feeling really tired and then suddenly it hit me, that was exactly how I felt when I was pregnant with Teddy,' trained dancer Caroline explained to the mag.
'My mum went out and got a test and I left Adam downstairs while I took it. After I realised it was positive, I gave it to Teddy and told him to give it to Adam. I downloaded a pregnancy app and worked out that we got pregnant on our wedding day.'
The pair now intend to make their Christmas celebrations even more special by finding out the gender of their baby on 25th December.
'I've not cried throughout the pregnancy but if I find out we're having a girl, I will probably cry,' Adam admitted. 'I'm convinced we're having another boy so it'll be be quite overwhelming if I find out we’'re having a daughter.'
'Being a dad to a girl would be a lovely experience.'
Adam and Caroline have been together for nine years, with the actor popping the question during a romantic trip to Dubai in June 2016.
They said when their wedding took place in September that exchanging their vows had given them a 'special bond', particularly as their little boy got to be part of the moment.
'It was really important to have Teddy there with us during the ceremony,' said Adam at the time. 'Today is about all my family being together and I wanted to reflect that.'