New York plastic surgeon Dr Jon Turk described to People magazine how the "glowing" mum-to-be called her husband from the doctors while having her first ultrasound.
An excited Charlene telephoned Albert and said "We're going to have a baby!" Dr Turk revealed, adding: "They called him out of a meeting, and he was very excited, but then had to go back to the meeting."
CLICK ON PHOTOS TO ENLARGE
Princess Grace Foundation Trustee Dr. Jon B. Turk and wife Carolyn Gusoff with the royal couple
Minutes later, however, former Olympic swimmer Charlene, 36, had more exciting news for Albert – whom she wed in July 2011.
"She had to call him back when they saw a second baby on the sonogram," said Dr Turk. "He was busy in a meeting [and didn't know why she was calling] and reluctant to come out. But when he came out, she said, 'We're going to have two babies!' Two calls for two kids!"
Albert and Charlene's twins are due in December
Dr Turk, who is a trustee of the Princess Grace Foundation which was set up in honour of Albert's mother, said that the 56-year-old father-to-be is now focussing on getting the couple's homes ready for their two new arrivals.
"The princess told me that he's been walking around their residence and their summer house, starting to childproof the houses." he said. "He's worried about the corners of tables. And she's saying they're not even born yet! He's also going to put air in all the balls for soccer and basketball. He's already getting ready and it's still years away before they can play with a ball."
Zimbabwe-born Charlene cradles her bump
As for the gender of Albert and Charlene's bundles of joy, Dr Turk believes the couple are waiting to be surprised.
"When I asked him, 'Do you know what the sex is?' He said no," said the doctor. "I'm not sure if she knows, but I don't think he does."
According to the royal couple's friend they are "really excited" to become parents in December.
Dr Turk added that while expectant Charlene "gets a little tired at night", she has been taking things easy and is "well taken care of so everything is one hundred percent".