He will begin performances in the role of Guy Nov. 17 in the show, which is currently running at the Phoenix Theatre.

With Boyzone, Keating has sold over 25 million records worldwide and as a solo artist 20 million. Before joining the cast of Once, he will return to Australia for a fourth year as a judge on The "X-Factor."

In a press statement he commented, "I was truly bowled over when I first saw Once. The music and storyline are so incredibly moving and combined with John Tiffany's direction, I believe it's a modern-day masterpiece. It's unlike anything else I've ever seen.  When I was asked about playing the lead male (who is a busker in Dublin) I was completely overwhelmed because I knew it would be perfect - this was my home town, my people, and the place where I began my own music career. But as exciting as that is, it's scary too. I've never performed on the West End and this is a huge challenge and commitment.  I'm really looking forward to returning to London later this year and completely sinking my teeth into the role. I think there's going to be lots to learn and lots to gain from this experience and I just want to be the absolute best that I can be."

The current cast features David Hunter (Guy) and Jill Winternitz (Girl), who are joined by Fiona Bruce (Baruska), Jamie Cameron (Emcee) Mark Carlisle (Da), Matthew Ganley (Svec), Mathew Hamper (Andre), Daniel Healy (Eamon), Loren O’Dair (Reza), Miria Parvin (Ex-girlfriend), Tim Prottey-Jones (Billy), and Jez Unwin (Bank Manager).  Alternating the role of Girl’s young daughter Ivanka will are Juliana Cotton, Demi Lee, Gemma Loader and Ruby Payne.

To book tickets, which are currently on sale through July 4, 2015, contact the box office on 0844 871 7629 or visit Oncemusical.co.uk.