Given the enthusiasm with which Brian Cox campaigned for a Yes vote during the referendum campaign, his decision to quit Labour for the SNP may not seem surprising.
It is significant, though. Jim Murphy has made big play of wanting his party to be a place both Yes and No voters feel comfortable since becoming leader north of the border.
His mantra has been that Labour values still run strong and people should put constitutional politics to one side and focus on other policies.
Cox’s decision to quit slamming the party’s “empty rhetoric” and accusing it of selling out in the process severely dents those hopes.
Providing voiceovers for Tony Blair and Jack McConnell during previous election campaigns means Cox has by no means been a back seat supporter of Labour.
And, as one of the most popular and effective celebrities when it came to campaigning for independence, his defection to the SNP is a hammer blow to Labour’s narrative.
It is another blow to the party as it fights for its electoral lives amid desperate polling figures for May’s general election.
The Holywood actor’s declaration may not in itself seem shocking or significant, but it symbolises much bigger issues.