Despite promising himself he wouldn't become teary eyed like other reality show judges, the Welsh singer admitted that he struggled to keep his soft side hidden during filming.
"I'd seen judges on other shows crying and I’d always thought it was a load of rubbish but, when you're faced with sending someone really talented home, it's very sad," Tom explained ahead of Saturday's opening show.
He added: "The more you try not to cry, the harder is to keep it in!"
Sir Tom, who is joined by Jessie J, Will.i.am and Danny O'Donoghue on the new BBC One series, also explained how he had been knocked back by his looks early on in his career.
He said: "When The Beatles got famous, everyone was told they had to look like them. So I had record execs telling me to change my hair, because the curls didn't work!"
The Voice UK launches on BBC One on March 24 on BBC One.