The opening of the Wizarding World of Harry Potter saw attendance at Islands of Adventure rise by as much as 36% in 2010.
According to Jason Garcia of the Orlando Sentinel, this had resort executives pondering "when to expand Wizarding World and how to keep business balanced between Islands and Universal Studios Florida".
In April 2011, Brady MacDonald of the Los Angeles Times mentioned that rapid attendance growth led to speculation that The Wizarding World of Harry Potter would see a significant expansion, which would include Diagon Alley and a Gringotts-themed dark ride possibly replacing the Lost Continent themed area in Islands of Adventure.

On December 6, 2011, Universal Parks & Resorts confirmed expansion plans but did not reveal specific details.
The announcement was made just four days after Universal revealed plans to permanently close the Jaws attraction.
Following its closure the following month, the Los Angeles Times stated that the site of the former Jaws ride in Universal Studios Florida would be used for The Wizarding World of Harry Potter expansion, despite what previous speculation suggested.
These rides would be complemented by a replica of the Hogwarts Express to move guests between the two parks.
Demolition of the Jaws ride and the Amity area began almost immediately after their closure.
After the site was leveled, work began on land reclamation in the area's former lagoon, as well as construction of a series of buildings including a large show building.

Further details about the expansion of the Wizarding World of Harry Potter were announced on May 8, 2013.
Officials confirmed that the expansion would be set predominantly in the adjacent Universal Studios Florida theme park, and would feature areas themed after Diagon Alley and London.
The rumored Hogwarts Express connection between the two parks was also confirmed.
Officials stated the expansion should open in 2014.

On January 23, 2014, officials announced the name of the flagship roller coaster would be Harry Potter and the Escape from Gringotts.
They also indicated that a two-park pass would be necessary to ride the Hogwarts Express, which was set to connect Universal Studios Florida with the existing Harry Potter area at Universal's Islands of Adventure.

The official opening date of the Diagon Alley phase was announced at an exclusive and private press conference on June 17, 2014, for July 8, 2014.
On June 18, 2014, the Diagon Alley red carpet premiere took place with Domhnall Gleeson, Bonnie Wright, Evanna Lynch, Matthew Lewis, James and Oliver Phelps, Tom Felton, Robbie Coltrane, Warwick Davis and Helena Bonham Carter attending.
New photos of Diagon Alley were later released the same night and the official opening date was  announced publicly by Universal Orlando's president, Bill Davis.
King's Cross station opened on July 1, 2014, as well as the Hogwarts Express Hogsmeade Station at Islands of Adventure and soft openings of Diagon Alley began on July 3, 2014.
Diagon Alley officially opened on July 8, 2014.
The opening of the Wizarding World of Harry Potter saw attendance at Islands of Adventure rise by as much as 36% in 2010. According to Jason Garcia of the Orlando Sentinel, this had resort executives pondering "when to expand Wizarding World and how to keep business balanced between Islands and Universal Studios Florida". In April 2011, Brady MacDonald of the Los Angeles Times mentioned that rapid attendance growth led to speculation that The Wizarding World of Harry Potter would see a significant expansion, which would include Diagon Alley and a Gringotts-themed dark ride possibly replacing the Lost Continent themed area in Islands of Adventure.
On December 6, 2011, Universal Parks & Resorts confirmed expansion plans but did not reveal specific details. The announcement was made just four days after Universal revealed plans to permanently close the Jaws attraction. Following its closure the following month, the Los Angeles Times stated that the site of the former Jaws ride in Universal Studios Florida would be used for The Wizarding World of Harry Potter expansion, despite what previous speculation suggested. These rides would be complemented by a replica of the Hogwarts Express to move guests between the two parks. Demolition of the Jaws ride and the Amity area began almost immediately after their closure. After the site was leveled, work began on land reclamation in the area's former lagoon, as well as construction of a series of buildings including a large show building.
Further details about the expansion of the Wizarding World of Harry Potter were announced on May 8, 2013. Officials confirmed that the expansion would be set predominantly in the adjacent Universal Studios Florida theme park, and would feature areas themed after Diagon Alley and London. The rumored Hogwarts Express connection between the two parks was also confirmed. Officials stated the expansion should open in 2014.
On January 23, 2014, officials announced the name of the flagship roller coaster would be Harry Potter and the Escape from Gringotts. They also indicated that a two-park pass would be necessary to ride the Hogwarts Express, which was set to connect Universal Studios Florida with the existing Harry Potter area at Universal's Islands of Adventure.
The official opening date of the Diagon Alley phase was announced at an exclusive and private press conference on June 17, 2014, for July 8, 2014. On June 18, 2014, the Diagon Alley red carpet premiere took place with Domhnall Gleeson, Bonnie Wright, Evanna Lynch, Matthew Lewis, James and Oliver Phelps, Tom Felton, Robbie Coltrane, Warwick Davis and Helena Bonham Carter attending. New photos of Diagon Alley were later released the same night and the official opening date was  announced publicly by Universal Orlando's president, Bill Davis. King's Cross station opened on July 1, 2014, as well as the Hogwarts Express Hogsmeade Station at Islands of Adventure and soft openings of Diagon Alley began on July 3, 2014. Diagon Alley officially opened on July 8, 2014.
The Wizarding World of Harry Potter (Universal Orlando Resort)