The rap star told Rap Radar in a podcast released Friday the couple’s new baby girl was named after the 13th Century poet, Jalal ad-Din Muhammad Rumi.
"Rumi is our favorite poet, so it was for our daughter," JAY-Z said, confirming what many have speculated since the twins' names were first announced in June.
But the process for their son's name, Sir, was a little more organic.
"Sir was like, man, come out the gate. He carries himself like that," JAY-Z, 47, said. "He just came out like, Sir."
The Tidal music streaming service owner also revealed to Rap Radar how his and Bey's first daughter, Blue Ivy, 5, rapped on his "4:44" album, saying she climbed up onto a stool and started stringing together a rhyme.
“She got the headphones and she climbed on the little stool, and then she just started rapping,” he said. "I was like, 'Oh, s--t.' I have (her freestyle) on my phone. Five minutes! Five minutes of her doing that."