McGregor, 32, made the announcement on Instagram on Monday afternoon, sharing a photo of himself playing with his new bundle of joy.
‘The McGregor Clan is now a family of 5! Healthy baby boy delivered!’ he captioned the adorable picture. Baby Wonder Woman and Mammy Wonder Woman are doing fantastic!
‘God I thank you for everything you give to me and my family in this world. My newborn son, Rían McGregor ❤️.’
During a trip to Dubai earlier this month, McGregor and his wife celebrated their son Conor Junior’s fourth birthday in style.
The couple astounded their eldest child with a £500 Lamborghini Centenario, which he drove into the UAE hotel’s cultivation where they were staying.
McGregor has had a particularly happy month, as he topped Forbes’ Athletes Rich List in style on Thursday.
McGregor is the only Irishman to have reached the Forbes list, and is the first UFC fighter to do so.
After losing in a knockout in Abu Dhabi in January, McGregor will face rival Dustin Poirier on July 10 for the third time.