Fellow Bjork fans spotted the celebrity twosome roll up in separate cars, chatting through their windows before rendezvousing at the entrance to go into the concert.
The musical meeting comes after Rob and Katy's most recent unusual hang-out - 'crashing' a stranger's wedding rehearsal, where they quietly watched proceedings from the sidelines.
The singer seemed to have a rocking time, and, not mentioning her Rob rendezvous, she tweeted her die-hard fan love after the show: "Dear Bjork, how do I join your traveling girl cult? #brilliantshow".
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