(CNN)Jennifer Jones-Prothro and her husband James Prothro are expecting their ninth child in December, and she wanted this one's gender to be a surprise.
The Vacaville, California couple learned the gender of all of their other children before they were born. Each time, Jones-Prothro's dad, Charlie, would insist that they not tell him.
"My dad always wanted to be surprised by it," she said. "There are not many surprises left in the world these days."
Jones-Prothro's dad died last year after a long battle with cancer. When she became pregnant, she decided that she'd be surprised for him.
But when she was about six months along -- and her friends were excited to plan baby showers -- Jones-Prothro decided she wanted to know.
On Monday, she told her husband, who'd known the baby's sex for months, to come up with a creative gender reveal -- one that she'd never seen before.
This might seem like a huge amount of pressure, but Prothro is a creative guy and he wouldn't have wanted to do it any other way.
"It was more of a playful challenge," he said.
Prothro produces music and has a home recording studio. He also had voice messages from his father-in-law that his wife had saved when she realized her father was getting sick.
Prothro realized that he could edit the recordings so that his father-in-law could deliver the news.
"He was her everything," Prothro said, so there was no better way to tell her.
Prothro worked late into the night on Tuesday and was ready to make the big reveal Wednesday morning after they got the kids off to school.
"I was up late finishing it and I couldn't wait any longer," he said.
Although he was excited, Prothro didn't want to just spring the gift on his wife. Instead, he told Jones-Prothro to get ready and go downstairs because he wanted to record a video to share with their families.
In a video posted online, Jones-Prothro is seen sitting down holding a speaker.
"This is the most special, creative way I could think of to tell you the sex of our child, but I couldn't do it without a little help," Prothro is heard saying on the audio recording.
A second voice then says: "Hello, Jenny, this is your father. I want to let you know that it is a girl."
Jones-Prothro breaks into a smile, covers her face and begins to cry.
"The last person I expected to hear was my dad," Jones-Prothro told CNN. "I wouldn't have wanted to learn it any other way."
The video was uploaded to Twitter by the couple's 17-year-old daughter, Ana. She had only posted once before, but thought the 40 or so friends she had might like to see it.
Turns out, lots of people wanted to see it. The video has already been viewed 5.5 million times.
The couple said they're amazed by the reaction.
They haven't come up with a name for their daughter yet, but when they do, they plan to keep it a secret.
That way, Jones-Prothro said, they'll still have one surprise.