As means of communication and citizen participation, social networks are undoubtedly also today a way for the exercise of diplomacy. Therefore, we undertake this research with the aim of verifying how the highest diplomatic institutions in Spain and the United Kingdom are integrating the use of new technologies and, specifically, social platforms to connect with society, transmit transparency and proximity, manage their reputation, and exercise their role as national and international representatives of these States. Specifically, we compare the Spanish case with the British Royal Family, because it is the most popular reigning European monarchy among netizens. To do so, we analyse the adoption and use of social media by both royal houses. We identify the official profiles linked to them. We catalogue and study the content published by each institution. And we compare the practices carried out by them, finding that, although both institutions release institutional messages and leave a record of their diplomatic actions, the British Royal Family has been able to give a more personal, affable, and relaxed tone, acquiring a style more in tune with the participants of the networks.