| Type: | Bishop |
| Honorific-Prefix: | Most Reverend |
| Alonso Antonio de San Martín | |
| Bishop of Cuenca | |
| Church: | Catholic Church |
| Diocese: | Diocese of Cuenca |
| Term: | 1676–1705 |
| Predecessor: | Francisco de Zárate y Terán |
| Successor: | Miguel del Olmo Manrique |
| Consecration: | April 1676 |
| Consecrated By: | Francisco de Rois y Mendoza |
| Birth Date: | 12 December 1642 |
| Birth Place: | Madrid, Spain |
| Death Date: | 5 July 1705 (age 63) |
| Death Place: | Cuenca, Spain |
Alonso Antonio de San Martín (12 December 1642 – 5 July 1705) was a Catholic prelate who served as Bishop of Cuenca (1681–1705) and Bishop of Oviedo (1675–1681).[1] He was an illegitimate son of King Felipe IV of Spain.
Alonso Antonio de San Martín was born in Madrid, Spain on 12 December 1642.[2] [3] He was the illegitimate son of King Felipe IV of Spain and of a young woman who served in the Buen Retiro Palace, named Tomasa María de Aldana, a native of Illescas, Toledo. However, in the newborn's baptismal certificate, which took place in the parish of San Sebastián, are assigned as biological parents: Juan de Valdés and María Díaz.[4]
On 1 October 1675, he was selected by the King of Spain and confirmed by Pope Clement X on 16 December 1675 as Bishop of Oviedo.In April 1676, he was consecrated bishop by Francisco de Rois y Mendoza, Archbishop of Granada, with Clemente Alvarez López, Bishop of Guadix, and Melchior de Escuda Aybar, Titular Bishop of Utica, serving as co-consecrators. On 21 October 1681, he was appointed during the papacy of Pope Innocent XI as Bishop of Cuenca.He served as Bishop of Cuenca until his death on 5 July 1705.