The actor, who was promoting his new series "Carnival Row" on BBC Radio One on Monday (September 02), was blown away as 'Gemma from Hertfordshire' phoned in to offer up her best Katy Perry impression - but Gemma was actually the pop star.
As Gemma, Katy sang a rendition of "I Kissed a Girl", and Orlando confessed he was more than a little impressed.
"Gemma, that was great, really well done," Bloom said, insisting that he'd know that wasn't the real thing and adding, "It's hard for me, because I live with that voice."
Host Nick Grimshaw then revealed it was his real-life partner on the phone all along.
Katy pretended to be upset, stating, "I thought you knew me better."