Despite having a newborn baby at home, the Duke of Cambridge looked fresh-faced and relaxed as he chatted with guests including opera singer Katherine Jenkins and comedian Rory Bremner.
Guests congratulated him on the birth of his daughter Charlotte as he attended the star-studded reception at Windsor Castle.
Later William struck a far more serious tone as he urged the world to take “action” against the slaughter of animals for their body parts.
Speaking to dinner guests in his role as patron of Tusk, he said: “The plunder and destruction of Africa’s natural endowment remains one of the greatest challenges facing the world – and it is growing worse by the week.
“Over the last 100 years, the abundance of the world’s species has decreased by almost a third.
“But the picture in the last few years has seen a genuinely unprecedented rise in the numbers of animals being slaughtered for their body parts.