Spain's El Mundo newspaper has called on Queen Letizia to explain herself after leaked text messages emerged showing her supporting a prominent business executive caught up in a scandal involving alleged corporate credit card abuse.

The open letter published in Thursday's newspaper came after the digital publication eldiario.es reported on messages in October 2014 between Letizia and Javier Lopez Madrid, a longtime friend of King Felipe VI and former Bankia bank board member.

Letizia used an expletive to describe to Lopez Madrid the second of El Mundo that printed a story about him, adding "we know each other, like each other, respect each other."

Lopez Madrid is among former executives and board members being investigated for the credit card purchases.

Spain's royal palace doesn't dispute the texts.