14/03/2013 06:50 GMT

Simon Cowell Fails To Crack A Smile At Comic Relief 'Book Of Mormon' Performance (PICS)

It may be Red Nose Day on Friday, but Simon Cowell was not seeing the funny side at a gala in aid of Comic Relief last night.

The music mogul failed to crack a smile as he was joined by best pal Sinitta at a gala performance of 'The Book Of Mormon'.

The pair were joined by Simon's 'Britain's Got Talent' co-star David Walliams and his pregnant wife Lara Stone, who was looking radiant in a loose white frock which hid her bump.

Photo gallery 'The Book Of Mormon' Comic Relief performance See Gallery

Other celeb names at the bash included Kate Moss, James Corden and Claudia Winkleman.

But despite Simon's sour face last night, he has already done something funny to raise money - he is starring in a sketch with David set to air as part of Comic Relief on Friday.

Pictures released earlier this week gave a sneak peek and showed the pair getting 'married' following their long-running 'BGT' bromance...

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