The Spanish cabinet has met to begin setting out the exact steps for Prince Felipe’s accession to the throne following his father’s announcement that he intends to abdicate.
Spain has no precise rules regarding the process and so legislation is needed in parliament.
The parliamentary speaker Jesus Posada has said he believes everything should be sorted out by June 18.
King Juan Carlos and his son attended a military parade on Tuesday morning, appearing together in public for the first time since the abdication announcement.
Prince Felipe, who will become King Felipe VI, has long been groomed to succeed his father – but the country has seen no precedent for such an event since democracy was restored in the late 1970s.
The transition comes at a crucial time for the monarchy itself in Spain.
Thousands took to the streets of Madrid on Monday night, demanding a referendum on the monarchy’s future. Some waved banners with the slogan “No More Kings!”.
Prime Minister Mariano Rajoy has called on republicans to follow legal procedures if they want to change the rules, saying they have the right to try to amend Spain’s Constitution in parliament.