The black and white clip shows Katy sat at her bedside and telling her: "Grandma, it's Katy. I just wanted to tell you, I know you're not feeling well, but I wanted to share some exciting news with you.
"I'm going to tell you that I'm going to have a baby. I'm pregnant, Grandma!
"Katy is finally pregnant, she's the last one, but I have a baby inside me and I wanted to tell that to you."
Katy announced that her grandma had died on Twitter earlier this week. She shared a link to a version of song Deep Peace alongside the words: "a song for Grandma. May she rest in deep peace. Ann Pearl Hudson".
She also posted a tribute to her on Instagram, writing: "I don’t know when a soul enters a new vehicle but if there is an afterlife where there’s a waiting room of the coming and going my mind wonders if the soul that is waiting to come into my world is getting a kiss on the forehead from my sweet Grandma that departed this earth yesterday. My heart hopes so."
Katy announced that she was pregnant last week in music video for her latest single, Never Worn White. At the end of the video, she showed off her blossoming baby bump - and shared the clip on Twitter with the caption: "see us in 6 years with a full family tree".