Thanks for the pictures and back ground info - all interesting stuff.
SH was part of a brood of three from the Holkham Estate in North Norfolk. As you correctly stated he was a male, with one of each sex for his siblings. SH was seen not far from you at the RSPB reserve at Blacktoft Sands on 12.05.2015, but no sightings in the intervening 11 months. His sister was seen on and off around Rutland Water in 2014, then at Claxton, near Norwich in November 2015. No sign of his brother since shortly after fledging.
Thanks again Graham,