Rihanna's Diamonds World Tour hasn't been the smoothest ride. For the third time in just over a month, the 25-year-old had to cancel a show due to health issues.

Rih Rih was billed to hit Houston's Toyota Center Monday (April 15) but nixed the show "as a result of illness," according to tour promoter Live Nation. The company provided no further insight into her ailments.

Although refunds are available via the Toyota Center, fans were given the option to keep their tickets for a rescheduled show.

With a night off from work, the "Pour It Up" singer took to Twitter to send out prayers and well wishes to the victims of the Boston marathon bombing yesterday. Like many around the world, the Bajan beauty was saddened by the explosion, which killed three and injured more than 140. "Praying for the fallen soldiers," Rihanna wrote.

She never mentioned being ill.

The Diamonds World Tour kicked off in Buffalo, NY, on March 8. Days later, Rihanna cancelled her Boston show due to laryngitis.

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 (Photo: Jason Merritt/Getty Images)