Paula Abdul's plans to surprise her pal Simon Cowell at his 50th birthday bash have been ruined by a bout of influenza.

The singer was invited to help her former American Idol judge celebrate the landmark birthday at a lavish $1.5 million party in Hertfordshire, England on Saturday but after coming down with flu, she's currently recuperating in bed on doctor's orders.

And the star is devastated she won't be able to see her friend on his big day.

She writes, "Mama is sick. Up all night with the flu. I feel terrible. I knew I should've gotten the flu shot. Gotta get better... I even had a funny surprise in store for him.

"Not making it to the party after all. Dr. said no way. I'm bummed (but) I'll survive."