The soap star announced the exciting news on his Twitter page on Tuesday.
"My hero @karenmckay1 gave birth to our 2nd little dream Mason Mac Taylor Dawson this morning!!," he wrote, "Thx for all the support. We are thrilled XXX"
Newborn Mason is a little brother to their two-and-a-half-year-old son Buddy.
A few hours after sharing their happy news, he wrote another heart-warming tweet.
"Massive shout out to all the mummy's in the world! You really are just unbelievable! XXX #officiallyhumbled"
The small screen actor, who plays Darren Osborne in Hollyoaks, has been awaiting the arrival of his second child while squeezing in rehearsals and filming for Strictly Come Dancing.
Last week, his dance partner Ola Jordan revealed in her HELLO! Online blog that Ashley had been waiting on tenterhooks for a phone call from Karen.
"His fiancée Karen was due to give birth on Thursday, so he's had the phone on all the time in case she rings," she wrote.
"So, it could happen at anytime! If his baby is born during a live show, his mind will be all over the place. It's quite scary for him – and for me as well and it's not even my baby!"