  BL Lacertae is a blazar at the redshift of z = 0.069, eponym of the BL Lac
blazar type. It is also a prototype of the low-frequency-peaked BL Lac (LBL)
subclass. It was first detected in sub-TeV gamma-ray range by MAGIC in 2005. In
2015, MAGIC observations of BL Lacertae were triggered by the Fermi-LAT
analysis report in the MAGIC group, and were performed during 10 individual
nights between 15th and 28th June for a total of 8.6 h. The measured gamma-ray
flux varied from 40\% to 10\% of the Crab nebula flux above 200 GeV in the
nights from 15th to 17th June. In particular, a fast variability was found
during the nights of 15th and 17th June. % with a halving time scale of
(33+/-9) minutes, statistical errors only. We also performed multi-wavelength
(MWL) observations in the radio, optical, UV, X-ray and gamma-ray bands, and
%the MWL light curves indicate that the very high energy gamma-ray flare was a
so-called orphan flare, %i.e. no simultaneous activity in other wavebands was
observed. the MWL light curves indicate that no apparent simultaneous activity
in other wavebands accompanying the very high energy gamma-ray flare in June
2015 like an another occurrence of an orphan very high energy flare. In this
proceedings we will present the results of the campaign and discuss their
implications on our understanding of the object.
