'Never Really Over' hitmaker Katy, 34, recalled how the 'God is a Woman' singer got their bill at a sushi restaurant where they had a ''long meal' with Orlando's eight-year-old son, Flynn - whom he has with ex-wife Miranda Kerr - before they even asked to pay.
Appearing on the 'Ellen K Morning Show', Katy said: ''Two weeks ago, I was at sushi and I ran into Ariana Grande.
''At the end of my long meal with Orlando and his son, we finished after an hour-and-a-half and we asked for the check.
''They were like, 'Ariana Grande has taken care of it.'
''And we were like, 'Oh my god! That is so cool!' Orlando's son is eight, so he was like, 'Dope.'''
Katy's fiancé told her he has ''mad respect'' for the 26-year-old pop superstar after the ''cute gesture''.
She added: ''But that is such a boss move and such a cute gesture.
''Orlando was like, 'Man, I have such mad respect for her.' She was so kind. I love little things like that.''
Meanwhile, Katy also opened up about her latest single 'Small Talk', which is about the ''weird human experiment'' you go through before ''finding the one''.
She explained: ''It's such a bizarre thing that we have to go through, not all of us, some people get lucky and marry their first love and stay with them forever.
''If you're in the dating scene and you haven't landed on the one, you go through this weird human experiment where you reveal your whole self to a person, you are so intimate with them and sometimes it doesn't work out.
''You move on with your life, but you end up bumping into them.''