There are currently temporary traffic lights around this junction. Work is expected to be finished on the 15th June 2019.
These roadworks are now for the junction improvements that will provide a cycling route to/from the cycle lanes of Royal College Street (North) to/from Prince of Wales Road via castle Street.
Here are links to the proposed infrastructure improvements scheme:
CCC response and Officer's report: http://camdencyclists.org.uk/2018/03/kentish-town-road-rcs-castle-road/
Status info from Camden Council: http://find.camden.gov.uk/streetworks.aspx?area=kentish%20town%20road
The initial works were for Virgin Media presumably preparing for the main changes.