Williams is currently on the European leg of his "The Dear G.I.R.L. Tour" and was expected to perform in Barcelona's Palau Sant Jordi on October 1st then three days later in Madrid's Barclaycard Arena.
But an abrupt notice on Twitter from his PR agency cancelling the concerts has crushed fans' hopes.
A third concert in Lisbon, Portugal, was also axed according to Spanish daily El Periodico.
The promoter, Live Nation, said that those people who have already bought tickets for the cancelled gigs could get refunds from the point of purchase,
41-year-old rapper, singer, songwriter, producer and fashion designer Pharrell has won seven Grammy awards. His song "Happy" topped the charts in 19 countries, including Spain. It sold over 10 million copies, making it one of the biggest hit singles of all time.