The pair start the tour in London on Thursday evening and are also currently at number one in the singles chart with Long and Winding Road.
Gareth's unbearable!
But Will told Newsround that after the tour they will be doing their own thing.
And he joked about Gareth: "He's unbearable! I've said this time and time again but people think I'm joking! The man is unbearable!"
Friendly farewell
On a more serious note he said: "I think that after the tour we will go our separate ways.
"My album's coming out, his album will come out in the future. It's a nice parting - a friendly farewell!"
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