"Kevin will sign with Cardiff on July 1 and he's absolutely delighted about it," said Viola.
"There was a lot of competition for him, an English Premiership club, who I won't name, expressed an interest.
"But we got the impression he might not have been a first-team player there at the start and Kevin very much needs first-team football at this stage of his career.
"There were five or six Championship clubs who contacted us as well and a Norweigian and a Dutch side, but Cardiff City emerged as a clear favourite.
"Dave Jones, Sam Hammam and Peter Ridsdale all did a fantastic job of selling the club.
"I think Dave Jones was a major factor in the decision, he's a very good manager and well respected.
"When he spoke to Kevin he made it clear Cardiff are a club who are going places. Money wasn't an issue.
"They are moving to a new stadium, which is exciting, and there's a real belief they can do something in the Championship next season. Kevin very much wanted to be involved with that.
"He's been at Aberdeen since he was 11 and he very much felt this was the time he needed a change," he said.
"He wants a fresh challenge and Cardiff is perfect for that.
"If you look at the Championship this year, it's a very strong league.
"You've got the likes of Birmingham, Sunderland and West Brom who've come down and a lot of other strong sides, it's going to be very competitive.
"If you take Celtic and Rangers out of the equation, I think the English Championship is well on a par with the Scottish Premier League in terms of standards.
"Like any player, Kevin is ambitious and believes a move to Cardiff will be good for him.
"He's got two Scottish caps and is on the fringes of the international squad, but he wants to do better than that like any young man would."
"He's a great lad, a bit shy, but a real professional.
"He's one of those guys who does his talking on the pitch, he's very straight-forward a tough tackler.
"He will give all he's got to help his side earn a victory. I think the fans at Cardiff will take to him straight away."