It's about power; After Alex Salmond resigned as first minister, the plan was that Nicola would take over in Holyrood, and he would lead the SNP in Westminster, where he expected to be 'kingmaker' to a Milliband labour government and be in a coalition cabinet.

However, that didn't happen, and then Salmond lost his MP seat to a Tory.

Nicola felt threatened that he would seek to make a comeback in Scottish politics, as he has too much of an ego to come back and play second fiddle; she, the SNP leader and her husband, who is CEO of the SNP, couldn't control him.