Keith added to Britain's Grazia magazine: "You know it ain't over yet."
Katy became embroiled in Taylor's row with Calvin - who she split from in June, a few weeks before she began romancing Tom Hiddleston - after it emerged the Shake It Off hitmaker secretly wrote his track This Is What You Came For.
In a series of tweets, he wrote: "Hurtful to me at this point that her and her team would go so far out of their way to try and make ME look bad at this stage though,
"I figure if you're happy in your new relationship you should focus on that instead of trying to tear your ex bf down for something to do.
"I know you're off tour and you need someone new to try and bury like Katy ETC but I'm not that guy, sorry. I won't allow it.
"Please focus on the positive aspects of YOUR life because you've earned a great one.
"God bless everyone have a beautiful day (sic)".
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In response, Katy, 31, retweeted a message she wrote in May 2015 which read "time, the ultimate truth teller" and shared an animated Gif on Twitter of US presidential candidate Hillary Clinton pulling a smug "I told you so"-type expression.
And after Kim leaked footage of Taylor seemingly approving the lyrics to Kanye West's controversial track Famous, Katy plugged her new album and single, which are both called Rise, in a tweet which many fans took to reference the saga.
She simply wrote: "#RISE above it all (sic)"
- Bang! Showbiz
