mystery orange fruit

tiggywinkle starts with ...
Hi,
We have a tree on the property we're renting and have absolutely no idea what type of tree/fruit it is (neither do the owners). The tree is approximately 5m (I can't actually see the top as it is behind a couple of other trees). The tree has rough bark, leaves are glossy dark green tear drop shaped approximately 3-5cm in length. Very large thorns ~ 8cm in length. The fruit are small orange coloured fruit ~ 3-5cm round. The skin is smooth, almost like that of a loquat but the flesh is like that of an apricot. The skin is a bit bitter and the ripe fruit is very sweet (unripe is very bitter). They have ~5 seeds shaped a little like orange pips but the flesh sticks to them like in plums. It's been fruiting for at least the last 4 months... any ideas? I think it would make amazing jam :P

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