Sam Smith says "at the top" with Bond film "Spectre" song

After months of speculation, Grammy Award winner Sam Smith confirmed on Tuesday he will sing the theme for the next James Bond movie, "Spectre", the first time in 50 years that a British male solo artist has recorded the title song for a 007 film.

The "Stay With Me" singer co-wrote the track, "Writing's On The Wall", with fellow Grammy Award winner Jimmy Napes, with whom he collaborated for his best-selling 2014 debut album "In the Lonely Hour".

As he joins the likes of Adele and Shirley Bassey in performing a Bond film theme, Smith said he recorded the track late last year and found it difficult to keep the project a secret.

"It was harder than normal because everyone kind of guessed at the beginning and said it was going to be me and I had to just be really good at lying," the 23-year old told Reuters.

"(Recording the track is) at the top for me ... I never expected this to happen."

Speculation had mounted over who would sing the "Spectre" tune which, like Adele's Oscar-winning "Skyfall" theme, is likely to storm music charts around the world.

Other contenders had included Ellie Goulding and Radiohead -- with one British bookmaker suspending bets after someone tried to place a 15,000 pound wager on the band getting the gig.

The last solo British male to sing a Bond theme was Tom Jones with "Thunderball" in 1965.

"I wanted to inject as much me as I could into the song and then dress it in a Bond way," Smith said. "I sing love songs ... and that's what I wanted to do."

Daniel Craig reprises his role as secret agent 007 for the fourth time in the film directed by Academy Award winner Sam Mendes. The film, out this autumn, also stars Italian actress Monica Bellucci and Oscar winner Christoph Waltz.

Smith declined to say much about the song -- because it would give away the plot. The singer, who had vocal cord surgery this year, described how challenging it was to perform.

"It probably had something to do with it (his vocal chord problems) because ... the song is the highest song ever," he said. "It's so difficult for me to sing."

"Writing's On The Wall" is out on Sept. 25.

"Now hopefully me and Shirley can have a coffee," Smith said, referring to "Goldfinger" and "Diamonds Are Forever" singer Bassey.