The Parliament Speaker of Sri Lanka confirmed the development by saying he has received the resignation letter.

Colombo: Moments after Sri Lankan President Gotabaya Rajapaksa landed in Singapore after fleeing the country, the leader resigned. Meanwhile, the protestors, who had gathered at his home in Colombo and elsewhere, burst crackers to celebrate the moment.
The Parliament Speaker confirmed the development by saying he has received the resignation letter.
Days after announcement to resign from the top post, Sri Lanka President Gotabaya Rajapaksa and his family on Wednesday fled to Maldives. According to the reports, Lankan President Rajapaksa was received by Maldivian government officials at the airport in Male early morning.
As per the reports, Rajapaksa, his wife and few bodyguards boarded to a military aircraft late night on Tuesday. They took the aircraft from Colombo and left the country. In a bid to escape, his younger brother Basil Rajapaksa, too, has left the country. Earlier, former Finance Minister Basil Rajapaksa’s attempt to flee to Dubai was thwarted by protestors on the intervening night of Monday and Tuesday. He was barred by the immigration officials and he had to return.
It was reported that the President had urged Sri Lankan military to provide a plane for safe exit for his family which was accepted. After reaching at Male, he was taken to a safe location by Maldives officials under police escort.
The president of Sri Lanka enjoys immunity from the arrest but was feared action by authority after stepping down from the post. Though he had promised to step down on Wednesday but wanted to shift to another country before transition of the power. He was asking for peaceful transition of power in the country.