A statement was shared on his verified Twitter account with his 68,100 followers which read: "It is with our greatest regret that we have to tell you all that Ian has passed away today from severe pneumonia and multiple organ failure.
"He was in no pain and was surrounded by friends and family.
"He put up a good fight but is in a better place now. Roxanne."
The tweet was immediately inundated with well wishes to Ian's family from fans, friends and former colleagues.
One said: "Incredibly shocking and sad news. Hugs to you Roxy and the rest of the family. Ian was one of those unsung legends, he never gave up and despite his own struggles his outspoken outlook helped others. RIP Ian."
Another wrote: "OMG this is so sad, I've watched Ian's journey through the highs and very lows. How he seemed to be living life to its fullest, he's at peace now. Sending you a virtual hug Roxanne."
And a third added: "OMG this is so sad, many a time I had great times watching him perform, giving the judges stick and making the audiences laugh. Rest in peace Royce."
Last year, aged 50, Ian's showbiz pals including Ant McPartlin, Declan Donnelly, Simon Cowell, Olly Murs and Robbie Williams rallied behind him as he opened up about his rehab stint.
In an emotional statement, the ITV favourite said: "I just wanted to let you all know that my first 28 days of treatment have come to an end and I will now be going abroad for the next three months to continue my treatment and really work on me and issues that have been buried deep for 40 years."
He continued: "As well as my alcohol addiction I have also surrendered to my sex and love addictions stemming from my past which have affected my relationships greatly.
"I am committed to working on all of the above to be a better person to me and to others. I have f***ed up big time in many areas of my life and I want to apologise to everyone who was caught up in my 'madness'."
He went on to thank everyone who had stood by him and supported him both emotionally and financially, adding: "I know this is my last chance at life having been near death more than once."
Ian was best known as the warm up guy for ITV shows Britain's Got Talent and The X Factor.