According to Presidência da República, this visit to the Principality of Asturias is not a common gesture and it is a sign of personal esteem for the future monarch of Spain.
http://www.presidencia.pt/?id_categoria=9&id_item=1568
The last day of this State Visit to Spain started with a brief meeting with the Prince Felipe of Asturias, which was followed by a stroll by the historical downtown of Oviedo. The first stop was in the cathedral of the Asturian capital, with a musical moment interpreted by the choir of the cathedral and a visit to the Saint Chamber. Afterwards, President Cavaco Silva and Prince Felipe visited the Fine Arts Museum of Asturias, where theyinaugurated a painting exhibition by the plastic artist Adriana Molder, under the heading "Encontro Marcado".
Finally, the Prince of Asturias and the local authorities presented their farewell compliments to the President of the Republic and to Dr.ª Maria Cavaco Silva in the local airport, before their return to Lisbon.
http://es.news.yahoo.com/28092006/185/principe-ensena-oviedo-cavaco-silva.html
The Prince of Asturias accompanied the Portuguese President, Aníbal Cavaco Silva, for more than two hours by the streets of Oviedo, and said that his first-born, Infanta Leonor, won't attend prize-giving ceremony of the Prince of Asturias Awards, next October 20th, "because she is very small".
Cavaco Silva and his wife had the Prince as the best host for their route by the historical downtown of the city, which took them from the hotel Reconquista to the neighborhoods of the Fontán market, where they tasted the traditional cider "culín". The citizens, who were waiting for them along the route, applauded the retinue, congratulated Don Felipe for his future paternity, and asked about Doña Letizia, whose annoyances in the first months of pregnancy have prevented her to accompany her husband to her native land. "The Princess is well, very sorry for not being here", responded Don Felipe, before the insistence of the questions, which he wanted to avoid, so not to overshadow the protagonism of his guest, the Portuguese President.
Manwhile, he explained that the presence of Doña Letizia in the next delivery of the Prince of Asturias Awards in the Campoamor Theater of Oviedo will depend on how she will be by then.