At Apple's keynote address at its WWDC conference on Monday, it made a sly dig at Spotify. It was so short you'd miss it if you blinked.

So what was it?

When Apple debuted its new music streaming service, Taylor Swift was in the #1 spot on the video charts.

Taylor Swift famously does not get along with Spotify. She argues that its free, ad-supported model fails to properly value artists' work, and removed all her most recent music from the platform after a high-profile falling out. 

Shortly after she pulled her music from Spotify, her album 1989 sold 1.3 million copies within its first week the most of any album since 2002 and became the top selling album of 2014.

Apple Music, which will not have a free tier, does have Taylor Swift's music and the company not-so-subtly showed that off on stage.

What does Spotify have to say about all this? Spotify CEO Daniel Ek sub-tweeted to acknowledge he caught the dig, then deleted it. 

(Sub-tweeting is when you make a comment on Twitter that's obviously in reference to something, but you don't actually state the original the reference).

Here's what Ek tweeted:

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