Beforehand she said to The Evening Standard: "It's a really fun concept and it will be really interesting, but it is probably the gig I've done that's most out of my control. I have no idea how people will respond and most people on the Tube are so in their own world anyway that I don't know if people will respond."
"I get on public transport now and again, I mostly drive though. But I used to get the Tube when I was studying so I know what's it's all about. I always listen to buskers, but I've never busked before."
"We're trying to do something that's so far removed, I've always been quite a glamour girl. I really like my outfit but I've never performed in flat shoes and I'm normally in full on evening dress."
Afterwards, Katherine said: "I was really, really enjoying myself. On the initial first note I thought, ‘Oh God, I don’t know how this is going to work out. It was quite an operatic number and I wasn’t sure how it would be received.
"But by the second number commuters were stopping and some were moved to tears. The people were really lovely. One guy said I had made him late for work."
Katherine plans to donate the money she raised to a homeless charity, added: "It has got a great acoustic down there. I actually didn’t want it to end."
Did you see her perform on Tuesday? It's pretty clear from the video that the disguise didn't work and everyone recognised her. She even managed the amazing feat of actually getting people to pay attention to her on the Tube and not walk by as though having a superstar opera singer on the London Underground was an everyday occurance.