A Downing Street spokesperson said:
The Prime Minister met with Prime Minister Boyko Borissov of Bulgaria this afternoon. The meeting opened with the Theresa May welcoming him to London and congratulating him on his upcoming presidency of the European Council.
Borisov commented that the good relationship between the UK and Bulgaria will continue beyond Brexit and highlighted the strong security and defence cooperation between the two countries. Both leaders confirmed that this was a vital element of the UK-Bulgaria relationship and that both bilateral security cooperation and defence cooperation through NATO would continue.
They discussed the Western Balkans at length, noting that stability in the region was important to Europe as a whole. Both leaders recognised the important role of Turkey in the region. Theresa May notified Borissov that she would soon be inviting him to a conference on the Western Balkans to be held in London in July.
Brexit was discussed with the PM setting out her hope and expectation that the Council will confirm that sufficient progress has been achieved.
Link: Press release: PM meeting with Prime Minister Boyko Borissov: 11 December 2017
Source: Gov Press Releases