Letizia Ortiz has become Spain's first 'commoner' queen, much like Kate Middleton became for England. Apart from the obvious similarities between the duo - including their 'commoner' status, their relationships with their husbands, their attractive appearance, and their popularity among their country's population - they both share an astute sartorial sense, with their fashion being commented on and praised wherever they go.
E! Online has a feature on everything you need to know about Queen Letizia, including her background before becoming a royal. Letizia used to actually be a well-known TV presenter and reporter, and she did both her bachelors and masters in journalism. She was also married before meeting Prince Felipe, even though she got divorced from her previous husband less than a year after getting married to him. She's also from a middle class family [again, by royal standards], and she's very focused on charity, although that's considered a requirement for royals these days.
But even in addition to all of that, Letizia and Kate are mostly compared through their fashion choices, with Letizia taking the fashion world by storm over the past few months. Her choices over the coronation were widely praised, and she's always been able to take even 'regular' clothes and mix and match them to varying degrees of success. Much like Kate, Letizia's clothing choices will now be scrutinized during every major public appearance that she makes, and she'll have the power to make a designer's career just by wearing them while going shopping.
The one difference between Letizia and Kate that we've been able to note is that Letizia is technically spotted much more often in public than Kate is, but that could be attributed to the paparazzi in England being far more relentless in their pursuit of royals.