Great-grandpa-to-be’s reaction to pregnancy announcement has hearts melting

— -- When an Ontario, Canada, mom-to-be found out she was expecting, there was one very special person she couldn't wait to surprise.

Bianca Rollo has always been close to her grandfather, she told ABC News.

"I am the first grandchild. So my Papa [grandfather] and I have a different relationship than my brother and sister," she said. "When I was younger we would always do things together like go on boat rides at the cottage, motorcycle rides, garage sale shopping and go out for ice cream. He also adores my husband Ryan [Rawn] and our little Yorkie Audrey."

Still, Harry Rollo Sr., a.k.a "Papa," couldn't wait to have a "human grandchild," Bianca Rollo said.

In a touching video that's now gone viral, Bianca gives Papa a t-shirt that says "Great Grandpa to Be ... December 2017."

"I had the idea right away to make my Papa a t-shirt as I know how he loves his shirts and it would be something he would be so happy to wear," Rollo said.

In the video, Papa, 84, doesn't seem to quite appreciate the significance of the shirt at first. A moment later, however, he's moved to stunned silence and tears.

"I knew he would be excited and emotional, but I honestly didn't know what his exact reaction would be," she said. "I am so thrilled at how overjoyed he is about the news! I think this is the best news he and the family has had since we lost my Baba (grandmother) in 2008. We all miss her so much. It's exciting to be able to bring new life into this family."

As for Papa, he keeps referring to the baby as "she," Rollo said, though she and husband Rawn don't actually know the gender yet.

But when they find out, Papa will too. He's hosting a gender reveal party at his house in a few weeks.