Sancha Alfónsez, Infanta de Castilla y León - sancha is dother of Zaida

She was the mother of Alfonso VI of Castile's only son, Sancho,[4] who, though illegitimate, was named his father's heir but was killed in the Battle of Uclés of 1108 during his father's lifetime. It has been suggested that Alfonso's fourth wife, Isabel, was identical to Zaida,[5] but this is still subject to scholarly debate, others making Queen Isabel distinct from the mistress[6][3] or suggesting that Alfonso had two successive wives of this name, with Zaida being the second Queen Isabel.[7] Alfonso's daughters Elvira and Sancha, were by Queen Isabel, and, hence, may have been Zaida's.[8]

https://en.wikipedia.org/wiki/Zaida_of_Seville