The Constantinian Order enjoys an excellent relationship with the Sovereign Military Order of Malta and this dates back to the time when the Kingdom of the Two Sicilies historically enjoyed a close relationship with the island of Malta, with which it maintained a treaty granting military protection. Since 1878, every Prince and Grand Master of the Order of Malta has been a senior member of the Constantinian Order. The current and 79th Prince and Grand Master, His Most Eminent Highness Frà Matthew Festing has had a long association with the Sacred Military Constantinian Order of Saint George. Frà Festing served on the Council of the British and Irish Delegation of the Constantinian Order from 2002-2009 having been first invested as a Knight of Justice of the Constantinian Order of Saint George in 1991.
In 1994 the Grand Master of the Constantinian Order promoted Frà Matthew Festing to the grade of Knight Grand Cross of Justice. In 2010 the Grand Master further honoured him through his appointment as a Knight of Distinguished Royal Order of Saint Januarius and to Bailiff Grand Cross with Collar decoration of the Constantinian Order.
Until his death in 2008, the 78th Prince and Grand Master, HMEH Frà Andrew Bertie, was also longstanding knight having been invested by HRH The Duke of Castro into the Sacred Military Constantinian Order in 1985 as a Knight Grand Cross of Justice of the Order. Frà Bertie was later elevated to the rank of Bailiff Grand Cross with Collar in 1988 – the highest distinction within the Sacred Military Constantinian Order of St. George and in 1993 was invested as a Knight of Royal Order of Saint Januarius – the most senior Order of the Royal House of Bourbon Two Sicilies.
HRH Prince Ferdinando, Duke of Castro, the Constantinian Order’s Grand Master until his death in March 2008 was invested as a Bailiff Grand Cross of Honour and Devotion of the Order of Malta in December 1968. In 1988, the late Duke of Castro, also received from Frà Andrew Bertie, Prince and Grand Master, the rare award of an Honorary Cross of Profession. HRH Princess Chantal, Duchess of Castro, was promoted within the Order of Malta to the rank of Dame Grand Cross of Honour and Devotion in 1996.
HRH Prince Carlo, Duke of Castro, who first entered the Sovereign Military Order of Malta in May 1983, was promoted in February 2004 to the grade and dignity of Bailiff Grand Cross of Honour and Devotion.
HRH The Duchess of Castro was invested as a Dame Grand Cross of Honour and Devotion in October 2001.
Many senior officers of the Order of Malta across the world are members of the Constantinian Order and some hold official positions within the Grand Magistry of the Constantinian Order.