The 20-year-old came from a set down to beat Halep at Roland Garros in Paris and become Latvia's first Grand Slam champion.

Great Britain’s Margaret Scriven was the last unseeded player to lift the Suzanne Lenglen Cup in 1933.

After losing the opening set 4-6, Ostapenko was 3-0 down before an astonishing turnaround saw her come through to win the second and third sets 6-4, 6-3.

Ostapenko had never won a Women's Tennis Association (WTA) Tour-level title before and was playing in only her eighth Grand Slam.

En route to the final, she beat a string of higher-ranked players, including Australia's Samantha Stosur, Caroline Wozniacki of Denmark and Switzerland's Timea Bacsinszky.

"I cannot believe I am champion at 20 years old," said Ostapenko.

"It's so amazing to be here.

"I have no words, it is my dream. 

“I knew Simona was a great player.

"But I tried to play aggressive and everything turned my way.

"I fought for every point and I'm glad it finished my way.”

For Halep, who would have become world number one had she taken the title, the wait for a first Grand Slam victory goes on.

She was playing in her second French Open final, after losing in three sets to Maria Sharapova in 2014.

Action is due to conclude tomorrow with the men's final between Spain's Rafael Nadal and Stan Wawrinka of Switzerland.

Nadal will be aiming to win a record 10th title at the French Open while Wawrinka will get the chance to add a second Roland Garros crown to his 2015 victory.