The 48-year-old British-Australian actor and 39-year-old Dutch actress announced Monday on Twitter that they recently welcomed son Monte Pearce.
"A cute little package arrived and told us his name's Monte Pearce. We think we're gonna keep him," Pearce wrote.
Van Houten responded with a series of baby-related emojis.
Pearce and van Houten, who plays Melisandre on Game of Thrones, had confirmed the actress' pregnancy in March.
The couple jokingly made reference to Melisandre's sinister shadowbaby at the time.
"Ok. I'm ready for your shadowbaby jokes," van Houten tweeted.
"Nothing like the prospect of a shadowbaby to change your mind about becoming a father!" Pearce added.
Pearce and van Houten started dating after meeting on the set of "Brimstone" in 2015. The Western thriller co-stars Dakota Fanning and Kit Harington and will premiere at the Venice Film Festival in September.
"I'm working with the very talented and beautiful Carice van Houten," Pearce said of the movie in a 2015 blog post.
"The film's set in the 1800s and is about a Dutch immigrant family who've recently settled in the U.S.A."
Pearce split from wife Kate Mestitz in 2015 after 18 years of marriage.
Van Houten called it quits with director Kees van Nieuwkerk the same year.
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