Sein Ta Lone Mango variety is from Myanmar.  It is also known as the "Diamond Solitaire" or simply "Diamond", and "Priyoor" (in India). In Florida it is grown under name "Guava".
 
Taste: The yellow flesh is firm and juicy, the flavor is sweet and complex, offers an intense mango and guava-like taste, with some acidity and hints of resinous. Fiberless.
Fruit size: Medium (1 - 1.5 lb)
Tree size: Medium (15 - 20 ft tall)
Season: May - July
Myanmar variety