The 'Chained to the Rhythm' hitmaker appeared to leave little doubt as she flew into London to catch the 41-year-old actor live on stage as he stars in dark comedy 'Killer Joe'.
She revealed her trip on social media, sharing a snap of the programme for the production complete with heart emojis around his face as she sat in the audience at Trafalgar Studio 1.
The play - directed by Simon Evans - opened for previews on May 18, and will run for the public from June 4 to August 18.
Katy, 33, was only making a whirlwind stop in the UK to support her rumoured beau, as she will be performing herself in Amsterdam this weekend with two shows as part of her ongoing Witness Tour.
She has added fuel to the fire after confirming she is no longer single, after being romantically linked with the hunky actor - whom previously dated a year ago - once again over recent months
During the finale of 'American Idol' on Monday (21.05.18) night, Katy hilariously confessed her love for 'Bachelorette' star Becca Kufrin, who was a special guest on the show.
Getting down on her knees, she joked: ''Can I be in the running?''
Becca replied: ''Yes, I'll give you all my roses.''
To which Katy then added: ''I'm not single but I still like you.''
Her confession comes after she previously admitted she was ''spoken for'', but again refused to confirm whether her lover is Orlando.
Luke teased: ''Yes, Katy's like that. She totally could.''
But Katy replied: ''No, I'm sorry I have been spoken for and speak for myself. And I'm very happy!''
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