London, Dec 13 - U2 rocker Bono once wrote a song for music legend Frank Sinatra and serenaded him with it in a Mexican restaurant.

The pair became friends after Sinatra invited Bono to appear on his 1989 Duets album and the Irish rocker took it upon himself to write a song especially for the former, reports express.co.uk

Bono seized the moment to showcase the track, "Two shots of happy, one shot of sad", during a night out with Sinatra in Palm Springs, California.

"We went out with Frank to a Mexican restaurant and drank margaritas. I wrote a song for him, and sang it to him at the Mexican restaurant. Sadly he never recorded it," he said.

Bono and bandmate The Edge did get a chance to perform the song for Sinatra again at a special TV tribute to the star on his 80th birthday in 1995 and his disappointment was further appeased when the icon's daughter Nancy recorded a version of the track for her 2004 album Nancy Sinatra.