Leopold III of Belgium had an illegitimate daughter who is now 70 and lives in the US.

Alfonso XIII of Spain had two illegitimate children. The son became a military pilot and later struggled through several jobs. The daughter married but died at 40.

It is suspected that Prince George, Duke of Kent, had an illegitimate son with an American socialite. That son later went on to serve in the US Marine Corps in World War II and was wounded at Iwo Jima. He later married the younger sister of Jacqueline Kennedy, and after their divorce remarried Laura, Duchess of Marlborough.

Prince Ernst August of Lippe's first child was born out of wedlock, but the prince married the mother soon thereafter. The son claims headship of the House of Lippe despite his illegitimate birth.

Prince Leopold of Bavaria's first son was born out of wedlock, nearly five years before his parents were married. He is officially in the line of succession and currently works as a cardiology researcher in the US.

Prince Albert II of Monaco has two children born out of wedlock, now 22 and 10 years old. The 22-year old young lady has already established a humanitarian fund in Fiji and apparently enjoys a good relationship to her parents and stepmother.

Prince Jean of Luxembourg's first child was born out of wedlock however the prince soon married the mother.

Prince Louis of Luxembourg's first son was likewise born out of wedlock however the prince soon married the mother.