The duo has been working together on the British version of the singing reality show for sometime now and Walsh has seen Cowell go through some tough days.
"Yes, he's human and he has dark days like everybody else. I don't see him when he's like that; he goes off and keeps to himself," dailystar.co.uk quoted Walsh as saying.
The two are mostly seen pulling each other's leg during the show, but Walsh feels that they are very loyal to each other.
"Simon loves honesty. I'm always critical of him, and he's always slagging me off. That's why we get on so well. We're very loyal to each other, which is important," said Walsh.
Walsh and Cowell also share the judging panel with Sharon Osbourne and Nicole Scherzinger.
--IANS (Posted on 24-11-2013)