Ranbir Kapoor planned a special birthday surprise for his "Rockstar" co-star Nargis Fakhri up in the air when the duo was flying to Nagpur for the promotion of their movie.

Ranbir, Nargis, singer Mohit Chauhan and producer Hiren Gandhi were on board the charter flight when Ranbir brought out a cake for the lady Thursday.

The actor had pre-ordered a Ferrero Rocher chocolate cake from one of Mumbai's premium bakeries and quietly got it onto the flight without Nargis's knowledge, said a source.

While Nargis was sitting on her seat unaware, one of her staff members took her outside the cabin on some pretext. When she got back, the entire team yelled "Surprise", and presented the cake to her.

The team sang "Happy Birthday" for her, while an overwhelmed and emotional Nargis cut the cake.

The debutante, who turned 32 Thursday, fed the cake to Ranbir and others.

All of them partied on board the flight listening to "Rockstar" songs, which have become a rage.

"Rockstar", directed by Imtiaz Ali, is produced by Shree Ashtavinayak Cine Vision Ltd and Eros International. It will release Nov 11.