The festivities will throw the spotlight on the king's oldest daughter Leonor, the 12-year-old heir to the throne.
Felipe will award the angelic-looking princess with one of Spain's most prestigious awards, the Order of the Golden Fleece which dates from 1430, at a ceremony in Madrid.
To mark his birthday, the Royal Palace over the weekend released dozens of photos and videos providing a rare glimpse of Felipe's domestic life with his wife Letizia, a former TV anchor, and their two young daughters.
They show Leonor in her school uniform holding Felipe's hand, laughing while eating soup at the family dinner table, and teasing the king just before he taped his annual Christmas message.
The images are meant to make the royal couple more relatable to Spaniards, in a country where the monarchy was only restored in 1975 following the death of longtime dictator Francisco Franco, and support for the institution is seen as shaky.
Felipe ascended to the throne in June 2014 after his father Juan Carlos, weakened physically after health issues and tainted by scandals, decided to step down following a 38-year reign.
It was the first time in five centuries that a Spanish king had abdicated in favour of his son.
The transition was handled quickly to avoid a risky debate over the continuation of the monarchy.
“Unlike other European countries, Spain is not monarchist in its DNA,” Ana Romero, a journalist specialising in Spain's royal family, told AFP.
Felipe “could restore dignity to the institution and behave impeccably but if part of the population insists on having a referendum to choose between having a monarchy or a republic, the outcome would not be certain”, said Romero who has just published a book about the king.
Felipe is reputedly cordial, well informed and thoughtful, although less charismatic than his father, who is credited with helping to steer Spain to democracy following Franco's death.
One of Felipe's toughest moments came when he had to distance himself from his sister Princess Cristina whose husband, ex-Olympic handball player Iñaki Urdangarin, was found guilty last year of siphoning off millions of euros.
More recently, the king's short reign has been tested by the ongoing crisis over Catalonia's breakaway attempt in December.
On October 3rd, two days after the region held a banned independence referendum, he gave a forceful defence of national unity during a televised speech.
In his strongly worded address, Felipe said the Catalan government had “systematically violated the law, demonstrating a disloyalty that is inadmissible”.
However, he made no mention of the police violence that had marred the referendum — an omission that disappointed many Catalans who saw it as the king siding with Prime Minister Mariano Rajoy's conservative government.
“The king is the head of state. It would be really strange if he did not defend the constitution and did not denounce certain events,” a royal palace spokesman said earlier this month.
'What's the monarchy for?'
Royal expert Romero said the king's speech “was decisive, to the degree that some people speak of it as the founding event” of his reign.
“In the majority of the country it was received with great applause” except for Catalonia, as well the Basque Country and neighbouring Navarre which also have active separatist movements, she said.
The address was also denounced by the far-left Podemos party whose leader Pablo Iglesias asked during a party gathering earlier this month: “What is the monarchy for?”
Felipe's big challenge is to make Spaniards “accept the institution as something established and which will remain forever as part of history”, said Romero.
By Laurence Boutreux / AFP