The singer insisted that it made no difference to their friendship that the R'n'B star couldn't make it to her wedding to Russell Brand last month because of 'work commitments'.
Perry, 26, told Now: 'I was upset she couldn't make it but let me promise you, there was no-one more upset about it than her.
'When you have an album coming out you don't have a spare second in the day and you're answerable to the record company.'
She added: 'She felt really bad she couldn't be there but we're still the very best of friends.
'My girl organised the best bachelorette party ever and I'll always love her to bits. It was just one of those really unfortunate things.'