The new family addition joins the couple’s two daughters, 2-year-old Inez and 4-year-old James.
It’s not clear when the baby was born, but it may have been nearly two months ago, Us Weekly reported.
The couple hasn’t yet publicly announced the birth or any details about the baby. Reynolds posted photos Friday on Instagram Stories showing a dinner date with his wife.
The couple, who married in 2012, revealed that they were expecting at the New York premiere of Reynolds’ film “Pokémon Detective Pikachu” in May. At the time, a visibly pregnant Lively joked on Instagram that she was a PokeMOM, adding: “Out now.”
Lively, now 32, indicated to People in 2016 that she and Reynolds, now 42, may have been hoping for a large-ish family. She was one of five siblings, and he was one of four.
She told Marie Claire the same year that they planned to raise their children as normally as possible.
“Ryan had a nice, normal upbringing, and we want our kids to have the same normal life that we had,” Lively said. “We don’t ever want to rob them of what we had, because we’d feel really selfish.”