Norwegian billionaire Torstein Hagen and his daughter Karine have increased their majority stake in Viking Holdings, primarily by exercising warrants that gave them rights to buy more shares.

The rising value of shares in Viking, a California-headquartered cruise ship operator, is approaching double their IPO price after just seven months on the New York Stock Exchange.

The Hagens’ Viking Capital reported holding nearly 235m shares in the cruise company, which equates to a 53.3%