Studies have shown that skin absorbs some of the toxic chemicals contained in consumer dyes.

These can pass through the bloodstream and to the foetus, potentially causing developmental issues.

Although doctors believe dying hair is safe during pregnancy, the lack of available evidence supporting this often sees women carry on with caution.

Since those photos in 2015, the Duchess has stepped out several times with her roots on show, demonstrating she was unfazed by the media coverage.