"You wouldn't want to sing with someone you didn't like. That would be miserable."
Michael Ball is reflecting on his partnership with Alfie Boe - an Avengers-style meeting of musical superheroes, which has become one of the industry's biggest success stories.
The duo first became friends after they appeared in a disastrous staging of Kismet at the English National Opera, but it wasn't until last year that they had time to make an album together.
Together they went on to become the biggest-selling album released in 2016, and a Christmas number one, to boot.
"It outsold the Stones, Elvis, Gaga, Little Mix," says Boe, still sounding slightly bewildered.
"You felt a bit guilty about that," observes Ball. "I was fine."
This is how Ball and Boe talk. They're a linguistic tag-team, riffing off each other's answers and competing to make the pointiest barb.
Their second album, imaginatively titled Together Again, has just gone to number one, beating The Stereophonics by the narrowest of margins (just 35 copies separated them).
"It's a little bit potty, isn't it?" says Ball. "We had no clue all this was going to happen."
Settling in for a chat on London's South Bank, the singers seem supremely relaxed - their combined 51 years in showbusiness inoculating them against media-trained stock answers.
As you'll soon see...
Aflie, it sounds like you're suffering from a cold.
Alfie: I know I got it from meeting and greeting fans.
Michael: Did you see that woman at HMV? [coughing and spluttering]. 'I'm dying but I couldn't miss you. Can you sign that? Could I have a kiss?'
And now you know why Michael Jackson wore a surgical mask in public.
Michael: But also because his nose was falling off...
Ahem. You toured together for the first time last year. What did you learn from that experience?
Alfie: Well, we travel on separate buses now… and we stay in different hotels. Sometimes different cities.
Michael: Genuinely? I learned it's better to share. We were carried along on this wave of excitement every day as the statistics came in, and new tour dates were added. I don't think I would have enjoyed it on my own. I would have felt a lot more pressure.
Why do you think Together became the biggest-selling release of 2016?
Alfie: We get asked that quite a lot but it's not something I want to focus on. Instead of analysing it, I just appreciate it.
It felt like there was an appetite for the music. Bradley Walsh had the best-selling debut album of the year, too, with a similar selection of covers.
Alfie: It wasn't that similar, was it?
Michael: No, he was more swing music.
Alfie: And he's ugly.
Michael: Nasty as well.
Alfie: The amount of botox he's had is ridiculous.
Do you realise you've now libelled two people in the space of five minutes?
Michael: Oh, we can libel Bradley. [Leaning into the microphone] Bring it on, Bradders.
Your new album opens with an incredible suite of songs from West Side Story. Did you record it live with the orchestra?
Michael: We did it the same way we do all the tracks. We sit and work the structure of it, then we put down a guide vocal...
Alfie: ...And then we play each individual instrument in the orchestra. Michael starts on percussion and I'm on the bassoon.
Michael: Do you know, my music teacher at school once asked me what instrument I wanted to play, and I said, 'the piano'. He looked at my hands and said, 'Hmm. Have you thought of the bassoon?' So I never learned an instrument.
Why the bassoon?
Michael: Because I have huge hands. Look at the size of those fingers! I mean, they're chipolatas.
Alfie: But big hands are good for the piano, aren't they?
Michael: No! I hit two keys at once.
Alfie: Les Dawson could play piano and look at the size of his hands. What about Fats Domino?
Michael: Literally, I'm about to punch him.
Did you get any encouragement in school?
Alfie: I wasn't encouraged to sing.
Michael: My school didn't want me in the choir because I couldn't blend! But luckily there was an English teacher who used to put on plays and I would get involved in those.
What was your first production?
Michael: It was actually King Lear. The sixth form were putting it on because they were studying it for A Level - and they brought me in to play the fool.
I'd already been to see it, actually. My dad took me to the RSC to see Donald Sinden do it with Judi Dench, and it just made Shakespeare come alive for me, before they ruined it at school. So I talked to this teacher about that and he said, 'Right, we're putting you in this production.' It was kind of a coup that a young whippersnapper was allowed to join the sixth form.
When we spoke last year, you said you wanted to do a Wham! medley. After George Michael's death, I thought you might have recorded one for the album - but I guess you decided against it?
Michael: Oh, but come to our tour and see what happens. I'm making him do it!
Which songs are you doing?
Michael: We're still working on it.
Alfie: I think we're starting with…
Michael [singing]: J-j-j-jitterbug!
Alfie: No! It starts with a real quiet one…
Michael: You know, the one that goes "do, do, dooo, dooo... had I been there."
A Different Corner
Michael: Yes! It's an amazing song. He was 16 when he wrote that. [Singing again] "They say loooove is a curious thing."
Alfie [scornfully]: You don't have to do that now.
Did you ever see George Michael play live?
Michael: Many times, and he was a brilliant live performer. That voice was clear as a bell.
There are a lot of really moving lyrics on the album. What's the one that resonates with you the most?
Michael: The Rose. It's a very personal song for the family. I recorded it for charity when my sister-in-law died. We started a charity for her - ROC, research into ovarian cancer - and I think the lyric is so beautiful and so poignant. And I'm so pleased Alfie did it, because he takes it over into a whole new dimension. I love it.
Do you hear songs and think 'this would be perfect for us to perform together?'
Michael: Yes, exactly. But we're both going to be doing solo projects next year, so obviously both of us are keeping things in the back pocket.
Will you be competitive about whose album does best?
Michael: I think we'll actually record the same tracks. The same album, same arrangement.
Alfie: And my album will be the harmony lines, so you'll have to buy both and play them together.
After Together and Together Again, will those solo albums be called Alone?
Alfie: Or, 'Having a Break'.
Michael: 'I Need Some Space'.
And will there be a third duets album?
Michael: We'll call that one 'Not Again'.
Alfie: I think a Christmas album would be cool.
Michael: Together at Christmas!
You could do an album themed around The Christmas Carol, with the songs of Christmas past, present and future.
Alfie: That's a really good idea.
Michael: I know one we'd have to do, because it's my favourite Christmas song: Oh, Holy Night!
Alfie: No, I'm not doing that one.
Michael: And for songs of Christmas future we'd have to have new songs. Let's write a Christmas song, Alfie!
Alfie: That'd be good. I can see the cover now. Bad sweaters, a golden retriever with antlers on, me dressed as Scrooge and Michael as the fairy on the tree.
Michael Ball and Alfie Boe's new album, Together Again, is out now. They tour the UK from 30 November.