Bob Crow was the greatest trade union leader of his generation and his death came as a devastating shock to me and millions of trade unionists.
I would like to send my union's heartfelt condolences to his family, friends and colleagues. I can't imagine how they are feeling and I hope the media respect their request for privacy.
Bob was without doubt a towering force in our movement. He represented the very best of trade unionism.
Under his leadership, RMT membership grew by 40% to 80,000 and wages across the rail industry increased faster than the national average.
But he was not just a skilled negotiator and strategist, he was a warm-hearted and funny man, and brilliant company.
We shared a love of football and he used to rib me ceaselessly about Millwall's supposed superiority over Cardiff. I have fond memories of him baiting me by text message as I stood in the away end in the bear-pit that is the Den.
His death leaves a very large hole but I hope we don't just mourn - Bob would have been the first to denounce us if we did.
I hope his legacy is a wider recognition that we need more people like Bob. People who fight tirelessly for rights at work, to improve pay and conditions, and against the relentless drive of privatisation that has proved so damaging to our rail industry that was so close to Bob's heart.
As is the case at times like these, political opponents are paying tribute in death to a man who they fought so hard to defeat while he was alive. It jars, but it is right that they do because it recognises Bob's huge contribution to public life.
It also reminds us what an enormous strength of character he had to withstand a level of sustained abuse and misrepresentation that no other union leader had to endure - and we get quite a lot.
Bob never let it deter him. In fact, it helped to spur him on because he knew if the bosses, senior politicians and the right wing press were on his back, the workers he represented were on his side.
Bob once asked why it should be just the bankers, the politicians and the idle rich who enjoyed the finer things in life. While some try to beat us by sowing the seeds of envy, Bob offered hope that a better world is possible.
I will miss him, the union movement will miss him and, if we don't pick up where he left off, society will be the poorer for his death.
Follow Mark Serwotka on Twitter: www.twitter.com/pcs_union