The Prince of Wales has sown seeds for a wildflower meadow named in honour of the Queen in London's Green Park.
Heir to the throne Charles joined school children to scatter yellow rattle flower seeds to start the new grassland.
As he strolled through Green Park close to his home, Clarence House, Charles was spotted by a pair of surprised joggers, who did a double take when they recognised the well-known royal.
He began the Coronation Meadows campaign in 2013 as a tribute to his mother to mark 60 years since she was crowned.
The project has created a new meadow in every county in the UK and the Queen's Meadow in Green Park is the 90th Coronation Meadow - and also marks the monarch's 90th birthday this year.
Over 97% of the country's wildflower meadows have been lost since the Second World War - amounting to nearly 7.5 million acres.
Charles, who is patron of the three charities running the project - The Rare Breeds Survival Trust, The Wildlife Trusts and Plantlife - joined local school pupils to sow the seeds, and met shire horses being used to harrow the ground.
The roots of the yellow rattle flower tap into those of the grasses around them, giving other wildflowers space to grow.
Rachel de Thame, Plantlife's vice president, called for the people to continue creating new meadows.
"The 90th meadow in London is just the beginning. We want to see the meadows revival reach every community and really start to restore the colour and diversity to our countryside," she said.
"And it's not just about the flowers - wonderful meadow plants like ragged-Robin, lady's mantle, burnet saxifrage and eyebright - but the wildlife they sustain.
"From bees collecting nectar from buttercups to goldfinches feasting on knapweed seeds and common blue butterfly caterpillars eating bird's-foot-trefoil leaves, if we all do our bit to bring wild flowers back - as I've started to do in my own meadow at home - we have a chance to help nature re-build its fragile balance and regain its full glory."