The 34-year-old model thought she and the 'La La Land' actress had become ''best buds'' after she spent a whole day interviewing her - but when they had a chance encounter soon afterwards, the Oscar-winning star didn't recognise her.
Speaking on Sean Evans' YouTube series 'Hot Ones', she said: ''I interviewed Emma Stone for my job, it wasn't like we were hanging out, which is the story.
''So I interviewed her and we went to this Museum of Curiosity in Brooklyn where you can dissect mice and learn about the Titanic, lots of different mysteries.
''She's amazing. So I thought we were literally best buds by the end of the day.
''And then I saw her another time and I was like 'Hi, hi', and she was like 'Hi'. [ with a glazed look on her face]. But not even an Oscar-winning actress can fake knowing me. I was like 'F**k'.''
Alexa has revealed she also met with mega stars before they became famous and had to remind Justin Bieber not to act ''cool'' around her, because she had known the 23-year-old singer when he was first starting his career.
She explained: ''The other thing was on my MTV show ['It's On with Alexa Chung'] we used to have Bieber on as a recurring guest because he wasn't a big deal yet. Bieber was on the verge of tilting into being [famous].
'' We used to call him Hug Boy because whenever I used to see him he used to give me a side hug, and we were like 'Urgh it's that kid'. That's crazy.
''Then years later I was interviewing him on the Golden Globes red carpet, and he was being too cool for me and I was like 'Excuse me Hug Boy, I think you're being a little too cool for me, we used to be buddies.' He was like 'Oh sorry'. ''
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