Pyongyang, North Korea - North Korean leader Kim Jong Un is believed to have turned 40 years old, though the milestone was not publicly acknowledged in the secretive country.

Kim’s birthday has never been revealed to the public, but if speculators are correct, he celebrated the event on Monday, the same day official pictures were released of him visiting a chicken farm with his daughter.

According to BBC News, the birthdays of his father Kim Jong Il (February 16) and grandfather Kim Il Sung (April 15) are celebrated as national holidays in North Korea. Kim, who took over as supreme leader in 2011, has not celebrated his birthday publicly like his predecessors, whose birthdays are notable for great fanfare and military parades.

Why Kim’s birthday has remained a secret is not known.

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In January 2020, North Korean officials thanked then-President Donald Trump for his birthday wishes for Kim but didn’t specify which day.

Around the same time in 2014, basketball player Dennis Rodman sang Happy Birthday to Kim in front of a crowd of thousands before an exhibition basketball game in Pyongyang. That remains the only public honoring of Kim’s birthday.

There are a number of theories as to why Kim hides his birthday. Some think it’s possible he does not want to draw unwanted attention to his deceased mother, who was born in Japan – a country North Korea distrusts.

However, that all may change in the future.

Kim Jong Il’s birthday reportedly became an official holiday when he turned 40 in 1982, but Kim Il Sung’s birthday became a holiday when he turned 56 in 1968.