The owner of Wimpy has snapped up the UK upmarket chain as the fashion for casual dining goes from strength to strength.
South African firm Famous Brands said it has signed "a mouth-watering" £120m deal to buy the chain from Nando's owner Capricorn Ventures.
The first Gourmet Burger Kitchen was founded in 2001 in Battersea, London, and the chain has grown to 75 outlets across the UK.
Kevin Hedderwick, Famous Brands' strategic advisor responsible for M&A activity said: "Quite simply, Gourmet Burger Kitchen is a best in class business and brand, with growing consumer equity, supported by a phenomenal leadership team."
"In terms of scale and scope, this is the biggest deal the group has ever concluded, and one which will transform the future of the business."
Famous Brands says it plans to double the amount of Gourmet Burger Kitchen's in the UK over the next five years. It said it plans to continue the chain's strategy of opening 10 to 15 new restaurants a year.
The South African group said: "The low interest environment in the UK is supportive of continued consumer spend, while the impact of fears of Brexit on this sector appear negligible."
Famous Brands, which also owns Salsa Mexican Grill and Debonairs Pizza, added that the burger chain will continue with its existing management team.
Alasdair Murdoch, chief executive of Gourmet Burger Kitchen, said: "We're delighted to move onto the next phase of growth with Famous Brands."
Gourmet Burger Kitchen was founded by three New Zealanders Adam Wills, Greg Driscoll and Brandon Allen, putting it at the forefront of the trend for upmarket casual dining.