Don Carlos Manuel Mariano Martínez de Irujo y del Alcázar, 8th Duke of Sotomayor, 3rd Marquess of Casa Irujo, Grandee of Spain (3 April 1846 – 14 September 1909) was a Spanish noble and politician who was an influential figure of the Restoration and of the regency of Queen María Cristina. 
Early life.
Martínez de Irujo was born on 3 April 1846. He was the only son of Gabriela del Alcázar, 7th Duchess of Sotomayor, and Carlos Martínez de Irujo, 2nd Marquess of Casa Irujo, who served as the Prime Minister of Spain under Isabella II from January to March 1847. His sister, María de la Piedad Martínez de Irujo y del Alcázar, married Pedro Caro y Széchényi, 6th Marquis of La Romana.
His maternal grandparents were Juan Gualberto del Alcázar y Zúñiga, 6th Marquess del Valle de la Paloma and Victoria María Teresa de Vera Aragón y Nin de Zatrillas, 2nd Duchess de la Roca. His paternal grandparents were the diplomat Carlos Martínez de Irujo y , 1st Marquess of Casa Irujo, and his American wife Sarah McKean (the daughter of the Pennsylvania Governor and signer of the Declaration of Independence Thomas McKean).
He studied law and became a diplomat.
Career.
In 1850, he became the 3rd Marquis of Los Arcos following the death of his father's younger brother. Upon his father's death on 26 December 1855 in Madrid, he became the 3rd Marquess of Casa Irujo. Upon his mother's death on 2 June 1889, he became the 8th Duke of Sotomayor. On 24 December 1890, King Alfonso XIII of Spain granted the accompanying dignity of Grandee to Don Carlos as third marquis.
In June 1897, the Duke served as Special Ambassador appointed by the Queen-Regent of Spain for Queen Victoria's Diamond Jubilee, attending the State Evening Party at Buckingham Palace on 24 June 1897.
He held various positions, including a member of the Congress of Deputies in 1876 and 1879 for the district of Ciudad Rodrigo with the ultramontane faction, and a Senator for the Logroño province in 1884 and, in his own right, since 1880. In 1902, he was made a Knight of the Order of the Golden Fleece. He was also a Knight of the Order of Santiago and of the Maestranza de Zaragoza, Grand Cross of the Order of Charles III. He was a Major Commander of León, Gentlemen of the Bedchamber Grandee of Spain and member of the Permanent Deputation of the Grandeeship of Spain. He was Sumiller de Corps from 1906 to 1909, Guardasellos de Su Majestad el Rey (Seal Keeper of His Majesty the King), Jefe Superior de Palacio (High Chief of the Palace), and Mayordomo mayor (High Steward) of the Queen from 1890 to 1906 (while she was Queen regent of Spain during the infancy of her son, Alfonso XIII).
Personal life.
On 28 May 1875 in Madrid, he married María de la Asunción Caro y Széchényi (1853–1897), a daughter of Pedro Caro y Álvarez de Toledo, 5th Marquis of La Romana, and Countess Erzsebet "Elisabeth" Széchényi (a granddaughter of Count Ferenc Széchényi). Her brother, Pedro Caro y Széchényi, 6th Marquis of La Romana, married Don Carlos' sister, María de la Piedad. Before her death on 7 September 1897, they were the parents of eleven children, four of whom died at an early age, including: 
On 11 March 1899, he married María del Pilar Caro y Széchényi (1864–1931), younger sister of his first wife and widow of the Marquess of San Felices, José María Guillamas y Piñeiro, Grandee of Spain, who died in 1895. Together, they were the parents of three children, including:
The Duke died on 14 September 1909 at San Sebastián. After his death, his widow, María del Pilar, remarried for the third time to the 12th Marquess of Martorell on 24 March 1922.