If you talk about physicality, I would think maybe Frederick. However, if you talk about strength of skill and technique, I absolutely have to say King Baudouin of the Belgians (you know - my guy

)
The following extract has been taken from the New World Atlas of Golf.
"No royal family has taken a livelier interest in golf than the Belgian. King Baudouin has represented his country in international matches, a unique distinction for a reigning monarch."
Baudouin was good enough to play the pro-am circuit. He played
rain or
shine.
Newsreel footage of Baudouin playing in a tournament (if the reel doesn't show, just click in the white space where it should be and it'll show up)
He was also a fan of fast cars and had an
Aston Martin DB2/4. Additionally, he had a
Porsche 356 Spyder and was a fan of Maserati as well. I hear he liked
motorcycles too, but don't have a picture of him actually on one. His
beautiful Aston Martin was restored and recently sold at auction in Europe for a lot of money.
Estimates were that it would be between €200,000 – 240,000.
He enjoyed
snow skiing,
tennis,
fishing,
hiking, etc. Hiking in particular allowed him to engage in his other passion,
photography. He was always game for trying out
various sport disciplines. His grandfather was the one who was killed while mountain climbing, so they all were pretty active. I also found information that he
qualified for and received his
pilot's license.
He also had interest in astronomy and not only
hosted the Apollo 10 crew and their wives but also
attended the launch in Florida. And, of course, he often played
chess and
billiards with Philippe and Fabiola.
Then, he had a life-long passion for and
commitment to
scouting and
remained active throughout his life in scouting events an
mentoring. This is no better evidenced than by the
Scouts of Belgium that showed their love for Baudouin at his
funeral.
But, you gotta love
Fabiola's sense of sportiness. I think about the only sport she did (besides billiards and very
minor cycling) was
spinning records on their player.
One small note about all of this...Baudouin suffered from
sciatic nerve flare-ups and later would advise his close assistants and house staff to never get into golf because it will ruin your back.
Together, they mainly did the billiards and
walking,
boating, swimming and
bicycling in Motril. In the mid-sixties, their boat, the
Avila was built and while it is sort of a
yacht, it was very much a working ship as well. Not fancy at all. Certainly not like Albert's or Juan Carlos' ships. They did, however, go on many many
vacations with Juan Carlos and Sofia on their boat. One thing I really like about Baudouin was that he had these
interests early in life and
maintained them throughout. I read that Baudouin taught Fabiola to swim - despite her growing up in a warmer climate, she could not swim and never put her bathing suit on as a young person.