Singer Bobby Hatfield, of the chart-topping duo the Righteous Brothers, died on Wednesday at the age of 63, his manager has said.
Hatfield (left) was found dead in his hotel room
Hatfield was found dead at a hotel in Western Michigan, half an hour before he was due to perform at a concert with singing partner Bill Medley.
The US pair had their first British number one in 1965 with You've Lost That Lovin' Feelin'.
They also topped the chart with Unchained Melody in 1990.
The group's manager David Cohen said: "It's a shock, a real shock."
He said Medley, who Hatfield had started the group with 42 years ago, was "broken up".
Hatfield's body was found at 2300 GMT.
Miller Auditorium executive director Bill Biddle told the audience minutes before the show the concert would have to be cancelled because of "a personal emergency of an unspecified nature".
Joe Hakim, an executive from the hotel Hatfield was staying in, said the singer had been sleeping most of the day. When he did not answer a 6pm wake-up call, staff entered his room and found his body.
The duo first found fame in 1964 with You've Lost That Lovin' Feelin'
The Righteous Brothers, who formed in California in 1962, first found fame in the 1960s, their debut hit being the 1964 single You've Lost That Lovin' Feelin'.
The song is said to have been the most-played song in radio history.
They also had hits with the songs Unchained Melody and Soul and Inspiration.
They broke up in 1968, but reformed six years later and went on to have another US number one with Rock and Roll Heaven.
They found new fame in 1990 thanks to the inclusion of Unchained Melody in the Hollywood film Ghost, starring Demi Moore and Patrick Swayze.
Earlier this year the Righteous Brothers were inducted into the Rock and Roll Hall of Fame.
British DJ Paul Gambaccini was among those who played tribute to Hatfield.
"Those two tracks will be remembered well into this century," he said of You've Lost That Lovin' Feeling and Unchained Melody.
"It's very rare that a person who is not a writer gets to perform in such a fashion and so memorably that his work is remembered for decades."
We asked BBC News Online users to send their tributes to Bobby Hatfield.
My deepest sympathy,may god give you strength at this sad time.
Sad that you've gone but know that you left a legacy, that song will be loved by future genrations. Not many of us can manage that.
Unfortunately death comes to us all but how fortunate to be remembered for such a wonderful song...!
Alex Osborne,England ( Uk )
Deepest sympathies to Bobby's family and friends - the world has lost a hugely talented and well-respected man whose truly brilliant songs will live on forever
Pippa,London - UK
His memory will always be remembered.
He and his songs will be remembered by people forever!
Hazel Lai,Hong Kong
One of the best all time classic songs, Unchained Melody. Copied but never equalled, he will be sorely missed.
May my God bless you with all the blessing he promised to Abraham.
Joćo Paulo de Sousa,Angola
What a complete shock - music has lost one of the all time best good guys, but he's left a tremendous legacy. My condolences and thoughts go to all the fans and Bill of course.
Ryan, Newcastle UK,UK
Very sorry to hear the loss of Bobby, his memory and music will live forever, god bless you Bill and your never forgotten singing brother Bobby.
Ben Walsh,Burnley, UK
What a sad day. Bobby Hatfield has given me so much happiness with the music he made with his brother. The music of the Righteous Brothers has always been with me. I have just introduced their wonderful songs to my daughter.
The Righteous Brothers made some of the greatest pop records ever. The superb mix of Bobby & Bill's voices backed by Spector's awsome production techniques were a real joy to listen to - then and now. God bless you Bobby.
Another piece of the past is gone. The music that stirred us, cheered us, stayed with us through our happy times, our sad times, will always live on. We will miss you Bobby as we increasingly miss so many of your contemporaries but we will all meet again one day. Thank you so much for so much. Rest in peace and God bless.
I will always remember him each time I hear your music .
You've lost that loving feeling still sends shivers down my spine all these years later. The sound of those two wonderful voices together will be greatly missed.
It's a real shame to lose a great addition to the music world. "Unchained Melody" is very famous in Egypt and loved by everyone. God rest his soul.
Unchained melody has got to be one of my all time favorite songs. I discovered it in the summer of 1989 when I first fell in love. It was & still is an incredibly moving, evocative song for me.
Go with God Bobby, thank you
The world has lost a phenomenal voice.
Mike Langridge,New Zealand
What a sad and very sudden loss. James Brown was the godfather of soul, but the Righteous Brothers were the godfathers of "blue-eyed soul". As soon as I heard the news, memories flooded back to the time I first heard "You've Lost That Lovin' Feelin; the year was 1965 and, as a very young toddler, was just starting to become aware of the records bought by my family, and sounds played on the radio. Our thoughts are with you Bobby........god bless.
So many inspirational singers have left us to play in the big band in the sky. He's up there with the greats, that moved our souls, inspired our minds and set our emotions free. They don't make music like they used to...to last a life time and more.
You've inspired a generation. Thankyou.
'You've Lost That Loving Feeling' will stay with me forever. God bless you Bobby. My thoughts are with you Bill.
B T,U K
My deepest condolences goes out to the family of Bobby. It is such a shame to lose half of a wonderful duo. Thank you for making fabulous songs such as Unchained Melody, and You've lost that loving feeling. Thank you for inspiring the world.
You will be missed. God Bless
Death comes to us all - we celebrate being born, we celebrate your departure but thank you for your gift of music which you have left behind to inspire us. You will never lose that Lovin' Feeling.
I remember imitating the song with my friend John Ryder as we waited to go into school in the mornings, in 1964/5. Happy days, and the song still brings back wonderful memories
He was and always will be remembered by one single word "Legend" Rest In Peace
Timeless songs... which will always be remembered. Thank you
May he rest in peace and may the world always remember his lovely music... This song will be still remembered for a long long time. All the strenght to his family and friends.
Liesbeth,Rotterdam, the Netherlands
I would be happy to die now if someone promised me that I would leave the same legacy as the Righteous Brothers to the world. Thanks for the memories.
We'll miss you Bobby, thanks for being so kind as to record your voice for us. We'll cherish it very much. Good luck upstairs !
An irreplaceable talent. My sympathy to his family and close friends.
Your songs have touched us in a many ways most of them good. I pray the good Lord will keep you close to His heart. Thank you and good bye!
zoilo cortes jr,Philippines
As a DJ and a great lover of Music, You've lost that loving feelin will go down in music history as a pop classic, and it is also sad to once again see the passing of a pop Icon, Rest in Peace Bobby.
Roger Jakes,England UK
The music industry has suffered a great loss. All my sympathies to his brother and family, his memory and song's will live for ever.
M Lawson.,London UK
My most lingering memory of theRighteous Brothers is their classic, the instant vintage Unchained Melody. With death of Bob that will sadly be confined to the screen. My condolences to the family and Bill who has lost one of the closest people he knew for almost half a century.
Larry Kwirirayi,Harare, Zimbabwe
A terrible loss. Unchained melody is one of the most beautifull songs sung by the most harmonic of voices. Now he harmonises with the angels. God bless and deepest sympathies to family friends and fans alike.
Unchained melody was the song that linked myself and the 'real love' of my life - the hairs on the back of my neck still rise when I hear the intro - revive wonderful memories!!
Thanks you so much for giving your fans endless pleasure. "You've Lost That Loving Feelin" comes high on the list of all time great hits. Rest in Peace.
A tragic and sudden loss to the music industry, their sound will never be repeated.
Even though we will not see you no more, your Tongue will be remembered for your great songs. May God find you a place in His Bosom (Heaven) Amen.
Clement Afum-Kuma,Ghana- West Africa
I think as a mark of respect there should be no re-releases this Christmas. let the music die with him . It's what he would've wanted
Chuck Connors ,waterloo , belgium
People don't understand why I'm crying at my desk here.
It's a tragedy.
One of the good guys.
I only met him once many years ago- when he was appearing on television with Roy Castle. A truly great man. Now both he and Roy are no longer with us. Sadly, sadly, missed.
A great loss- taken from us too early.
Goodbye good friend
A fantastic voice now sadly silenced. His version of Unchained Melody will never be bettered. Thanks for the music Bobby.
Ian Ross,Edinburgh, Scotland
I grew up listening to the Righteous Brothers through the films, Top Gun and Ghost and have listened to them ever since. I, among many, will miss Bobby dearly. Rest in peace.
The world will miss this talent, not only of Bobby, but of Bill. They both gave the world two of the best loved sing-along and emotion raising songs in music history.
Goodnight and God Bless Bobby Hatfield, may you rest in peace.
And let's not forget Bill Medley. May our prayers be with him through this most difficult of times.
A great loss to the music business. My deepest sympathy goes out to his friends and family in particular Bill Medley.
Jon Hope,United Kingdom
So sorry to hear this news today i loved your music as its my era too,and i love the song youve lost that loving feeling.
What a shock.Grew up with the Righteous Brothers' music!His Unchained Melody is second to none!!They never got the recognition they deserved Saw them live many times in the Buffalo area. Thanks Bobby,we will NEVER forget you.You are singing for God alone now..Rest in Peace
My thoughts are with the family. A true legend and inspiring singer song-writer. May his memory live on.
Bobby Hatfield was a true soul man and, along with Bill Medley, were favorites of mine growing up as a kid in the United States Midwest. We used to get a show called Shindig, as I recall, and the Righteous Bros. were featured regularly on the show with an incredible backup band, the "Shindogs" who had James Burton on guitar as I also recall.
But it was Hatfield's one line, "'Cause you don't love me like you used to do" in "You've Lost that Lovin' Feelin'" which still sends chills up my spine when I hear it. As soul music artists, he and Medley really had it in a time when not every soul singer did, even black ones. He and Medley had the gift of baring their souls musically which remains a rare gift in my opinion. I grew up playing that kind of music in bar bands and, believe me, that soul style took guts, hard work and a pure love I don't find in music today.
If this message could ever get to Mr. Medley, I would want to tell him he is, in my opinion, and remains a pioneer in a style of music and art still so vital, the world goes nuts over anyone who can remotely do what they were doing all along.
Robert W. Marcus,United States