Synonyms are Quercus x hispanica ‘Lucombeana’ and Quercus lucombeana.

Quercus x crenata is a hybrid between Q. suber (the cork oak) and Q. cerris (the Turkey oak). This cross has occurred several times. The two examples in commerce are the Fulham oak (also in Belfast Botanic Gardens) and the Lucombe oak. Both are semi-evergreen, often shedding some leaves in January or February.
The Lucombe oak is said to be distinguished by the fine points on the lobes of the leaves and by the ‘wiskers’ surrounding the terminal buds of its branches (photo below)
The Lucombe oak was discovered by nursery owner William Lucombe in 1762. True Lucombe oaks are clones of this original hybrid, but other similar hybrids are sold as Lucombe oaks. 
We don’t know the provenance of the Botanic Gardens specimen nor whether it a decendant of the true Lucombe oak or a similar hybrid. William Lucombe felled the original tree with the intention that the wood be used for his coffin. However he lived to 102, by which time his coffin planks, stored under his bed, had rotted.
Other fine examples of the Lucombe oak may be seen in Kew and Powis Castle.

Photos taken in Belfast Botanic Gardens in 2023. Copyright: Friends of Belfast Botanic