Beyonce has apologised for disappointing fans after cancelling her concert in Belgium.

The 'Grown Woman' singer was scheduled to perform at the Sportpaleis arena in Antwerp on Tuesday night (14.05.13) but had to pull out on medical advice because she is suffering from dehydration and exhaustion.

Beyonce posted a handwritten letter on her Facebook page saying sorry for her postponement but has promised to put on a great show when she takes the stage for her second scheduled 'Mrs. Carter Show' concert tonight at the Sportpaleis arena tonight (15.05.13).

In the letter, she said: ''To my dearest fans in Antwerp. I've never postponed a show in my life. It was very hard for me. I promise I will make it up very soon. I'm sorry if I disappointed you.

''Thank you for your concern. I'm feeling much better now and I'm ready to give you a great show. See you tonight.

''All my love, Beyonce.''

This week, rumours have spread that the 31-year-old star is pregnant with her second child with Jay-Z and her postponement was interpreted as the latest sign she is expecting.

Beyonce - who already has a 16-month-old daughter with the rapper - kicked off her 65-date world tour on April 15 in Belgrade, Serbia, and it is set to wrap up in Rio de Janeiro, Brazil, on September 13.