Fabian Picardo - until this week the darling of independence supporters and SNP allies in Catalonia and the Basque Country - declared his support for David Cameron's stance on Spanish television.
Repeatedly asked if he would support Scottish independence on a daytime chat show on the independent Antenna 3 channel, Mr Picardo said: "I defend the position of the Prime Minister, David Cameron."
Until his remark, the Gibraltarian leader has been a pin-up for Iberian minorities as he took on Madrid, which the UK claims has taken an increasingly aggressive stance over Gibraltar in recent months.
Gibraltar has twice held votes on its future, in 1967 and 2002 and on each occasion its people have backed British rule. Spain, however, does not recognise this. Catalan nationalists, in particular, have been inspired by Mr Picardo's battles against the staunchly unionist government of Spain.