And in the photo, which was posted yesterday (28 May), Katy has even given Adele the nickname of "Queen", saying: "…And on the 2nd LDN show the Queen graced me with her presence."
The gorgeous snap shows two of our favourite singers pouting away and looking stunning. Katy wears her hair pulled back off her face, emphasising her flawless skin and mega-watt lashes.
Meanwhile, Adele can be spotted in a cool black trilby hat and hooped earrings. She also made her peepers stand out with a black feline flick.
Katy has been over in London performing at the O2 as part of her 'Prismatic World Tour' and Adele popped down to watch the pop star doing her thing.
Earlier in the week, the 'Teenage Dream' singer also showed fans a picture from her actual show. The star looked amazing with rainbow-hued tresses and a dress embellished with multi-coloured butterflies.
Katy is no stranger to experimenting with her hair and clothes, just last month she dyed her locks a slime green hue!
As for Adele, she's been off the music scene for quite a while now, but hinted at the possibility of a new album very soon.
Hmm, anyone else sensing a possible duet could be in the works here? Fingers crossed…
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