When you walk along the streets of Brussels, you will find many Belgian flags hanging out of windows. In the city center, the biggest LED advertisement board has been changed from a Coca-Cola commercial into a huge black, yellow and red flag.

There are similarities between the flags of Belgium and Germany, but don't mention this to a German — you will be told that they are two completely different flags, and that German flag includes the color gold, not yellow!

Belgium's King Albert II (left) and his son Crown Prince Philippe share a laugh during a national ball in the Marolles district of Brussels to celebrate Albert's 20th anniversary on the throne on Saturday. Philippe Wojazer / Reuters

However, the two countries have a deep historical relationship. The first king of Belgium, Leopold I, was born in Bavaria, and refused the crown of Greece one year before he took an oath as the country's first king on July 21, 1831.

Only 13 days after King Leopold I took over the country, the Dutch army invaded Belgium. The seventh sovereign, King Philippe, 53, took the crown from his 79-year-old father, Albert II, on Sunday — and he will face pressure from Belgium's Dutch speakers.

King Leopold I did not force the country to use a united language, so French and Dutch are both official languages here.

Dutch-speaking Flanders, in the northern part of the country, has advocated the abolishment of the monarchy. By contrast, French-speaking Wallonia in the south has always strongly supported the king. So you will find there are many more flags hanging out of windows in the south than there are in the north.

From 2010 to 2011, there was a period when Belgium had no government for 541 days due to the split policies espoused by French-speaking and Dutch-speaking parties during the inconclusive 2010 election.

To help put the country back in shape, King Albert held countless meetings with politicians. A new government was finally formed on Dec 6, 2011, in which the Flemish separatist party N-VA has the largest representation in Parliament. It has advocated the restriction of royal powers.

On Saturday, King Albert made a public address and listed his hopes for the future, including a united Belgium and that the people would support his son.

"Give the future King Philippe and the future Queen Mathilde your active participation and your support. They make a great couple serving our country and they enjoy my full confidence," he said in a broadcast in front of a statue of King Leopold I.

Philippe's rule may be uncertain, but during the ceremony there were many people gathered in Brussels, shouting "Vive le Roi, Vive la Belgique!" There were all kinds of people there, and their support of the royal family was heartfelt.