The casual dining chain opened its first restaurant back in 1994, and has since expanded to 22 sites across Bulgaria, with a further two operating in Barcelona, Spain.
Signature dishes set to appear on the all-day menu in London include a deconstructed ‘broken burger’ made using British dry-aged beef.
"For us, the customer is sacred. We must meet their expectations and offer constant high-quality food and service,” says Happy founder Orlin Popov.
"We wish to become a restaurant that Londoners believe in and we want them to come back again and again.
"We look forward to opening our doors and showing [people] how we believe casual dining should be done.”
The menu will also feature a selection of roast chicken and steak dishes; as well as vegetarian and vegan options.
"London is one of the largest and most interesting restaurant scenes in the world, it's a dream come true to bring our brand here," adds Ivan Popov, who will act as general manager of the London restaurant.