Widnes said in a statement: “The Club believed that Kevin had earned the right through his outstanding contribution to our evolution both on and off the field to decide how we proceeded with the approach from Warrington.
“The Club sought Kevin’s instruction and he confirmed that he would like the Club to proceed with negotiations to allow him to take up a contract with Warrington Wolves for the 2017 season.
“Having received that instruction negotiations were concluded to facilitate the move.
“Widnes Vikings can therefore confirm that an undisclosed transfer fee has been paid and Kevin Brown has been released from his contract with immediate effect to enable him to join Warrington Wolves.”
Widnes CEO James Rule said: “This is not a situation we initiated or indeed could have anticipated at this stage in the off season.
“However Kevin has been an outstanding player, leader and ambassador for our Club over the last four years and we felt it was right to respect his wishes once he had confirmed he would like to take up a contract with Warrington Wolves.
“We can now look forward to being in a position where we can explore the available players that can enhance our team in the 2017 season.
“On behalf of myself, the directors, coaches, staff, Members, players and sponsors of Widnes Vikings, I would like to thank Kevin for his outstanding contribution to the Club and wish him and his family the very best of luck for the future.
“I am aware that a number of our stakeholders have been frustrated at the lack of commentary on the situation in recent days.
“This transfer had a number of moving parts and it was impossible to make any comment without risking undermining Kevin should the transfer have fallen through.
“The transfer was only finalised and signed off today (9th December) following Kevin’s completion of a medical with the Warrington staff.
“We are therefore communicating the news at the earliest possible opportunity.”
Mellor joined Widnes from Wigan Warriors in 2012 after a successful loan period.
Betts said: “Joe is a natural number 6. He has great talent and leads by example with his tremendous work ethic not to mention his drive and determination to succeed.
Betts has also given an indication as to what appears to be his favoured half back pairing for the new season by allocating the number 7 jersey to scrum half Tom Gilmore.
“I have spoken with both players about the prospect of re-issuing squad numbers and the response from both of them was fantastic.” he said.
“For Tom I think this is just reward for the patience and maturity that he has shown whilst waiting for an opportunity to cement his place in the Vikings First Team.
“Tom is a fantastic endorsement of our academy system and has been the stand out performer at every grade he has played.
“He has generated interest from a host of top clubs at every stage of his development. He has consistently rejected those approaches which clearly demonstrates his passion to represent his hometown team.
“As a Widnes lad, to run out wearing the number he has dreamed about from being a young boy will no doubt bring out the best in Tom.
“He has been a true professional, especially in the past few years as he has been chomping at the bit for an opportunity to stake a claim for a first team place.
“I have trust in him and am truly excited to see how he performs. For our members it will be fantastic to see another Widnes lad take to the field for his hometown club.
“I am sure that with the support and encouragement of all of our supporters Tom is going to prove that he is every bit the player that we all know he has the talent to be.”