Cabaret star Liza Minnelli marked what would have been her mom Judy Garland's 90th birthday on Sunday by giving a surprise performance in New York City.

The veteran entertainer was with pals at Carlyle Hotel's Bemelmans Bar to watch a gig by Jim Caruso and Billy Stritch when she was invited to step onstage.

Minnelli thrilled the audience as she wrapped up the show by belting out I Love A Violin, a track originally made popular by her godmother Kay Thompson.

A source tells the New York Post gossip column Page Six, "Jim just asked Liza if she wanted to sing, and the crowd cheered her to do it. That was the final song of the set. After all, how could they top it?"

It was a poignant day for Minnelli - her late mother Garland, who died in 1969, would have turned 90 years old.

The singer/actress took to her Facebook.com page on Sunday to pay tribute to The Wizard Of Oz icon, writing, "Mama gave each and every one of us the gift of hope, laughter and love." (PAW/WNWCPS/CL)