The 30-year-old defender this week completed a free transfer to Vicarage Road after five years at Pittodrie.
He told RedTV: "Of course.
"I said to myself if I get the chance to go at the end of my contract, I'd go.
"I've had five good years at Aberdeen. I had five at Hearts as well - so 10 years playing against the same teams.
"In that time, I could have played teams like Motherwell maybe 40 times.
"It's good to get a change and hopefully I can become a better player playing against better players."
"I actually knew quite a while ago when Malky first got the job," Severin said.
"But him being on his coaching badges, the club just had to wait until he was back to announce it."
Severin also had other options, adding: "There were a few teams interested but none of them would ever commit until about July 1.
"Then Watford came in and I was delighted to sign for them."