REBECCA ENGLISH: Though William's appearance today was welcome, you could see small signs of the toll recent months have taken on him... this is why we shouldn't expect a return to full duties any time soon

When Rachel Candappa kindly handed Prince William two cards wishing both his wife and father well in their individual cancer battles, his emotion was hard to miss earlier today.

Placing his hand on her shoulder, the future king looked the 71-year-old volunteer directly in the eye as she urged him to ‘take care’ of Catherine, saying firmly and repeatedly: ‘I will do, I will.’

He only swiftly changed the subject, I am told, when it became clear that Mrs Candappa was herself close to tears and the prince was at pains not to embarrass her in front of the cameras.

William’s visit to the Surplus to Supper food redistribution charity in Surrey was first time we have seen the heir to the throne in public following his wife’s unbelievably brave video message of March 22, when she revealed she has been undergoing treatment for cancer.

He was typically chatty, genial - laughing and joking with volunteers - but physically you could see small signs of the toll that recent months have taken on him.

William is given cards for his wife Catherine, Princess of Wales, and father King Charles by volunteer Rachel Candappa during a visit to Surplus to Supper in Sunbury-on-Thames, Surrey

William talks to van drivers during a visit to Surplus to Supper, in Sunbury-on-Thames, Surrey

William gets stuck in as he helps make bolognaise sauce with head chef Mario Confait

It is understood that William and Kate are both immensely ‘grateful’ for the space they have been given since her announcement.

The family spent the Easter break at Anmer Hall, their Norfolk retreat, where George, Charlotte and Louis were able to enjoy the country lifestyle they so love, as the ordinary children they actually are.

Indeed, only the couple’s closest aides have seen or even spoken to the prince or princess in recent weeks, emphasising the need for them to retreat and regroup as a family.

Back in October 2010, when he asked Catherine to be his wife, William had already privately promised her father, Michael Middleton, that he would do everything in his power to protect his daughter as she agreed to share his extraordinary - and very public - world.

Only the couple’s closest aides have seen or even spoken to the prince or princess in recent weeks, emphasising the need for them to retreat and regroup as a family

And he has been as good as his word, fastening a virtually impenetrable ring of steel around her and their children, in order to balance public duty with the family life that is so important to them both.

But cancer, as the Royal Family have sadly discovered in recent months, is a pernicious leveller that cares not whether it has prince or pauper in its sights.

And William has found himself facing a new battle: one that has struck at the very foundation of everything he holds dear.

One can only imagine the weight on his shoulders at seeing both his adored wife and his father facing serious simultaneous health crises, while also trying to protect his three young children from this devastating blow to their little world.

And while, fortunately, the King appears to be responding well to treatment and is hopeful of taking up more forward-facing public duties in the near future, recent events will have been a stark reminder of what awaits the Wales’ in the not so distant future.

It is why, although his appearances today were both welcome and heartfelt, we should not expect to see a wholesale return to royal duties for the prince.

Princess Kate making her cancer announcement last month

Instead, I understand, he is likely to undertake one or two public engagements each week - often on the same day in order to minimise time away from Kate and the children - as well as continuing with his usual behind-the-scenes work.

He will, I am told, almost certainly take some sort of role around the 80th anniversary of the D-Day landings in June, as well as attending Trooping the Colour and the annual Order of the Garter service and, perhaps, one of the annual summer garden parties for worthy community heroes.

And he will definitely continue to undertake investitures at Windsor Castle on behalf of the King over the coming weeks.

But he will also very much balance this with supporting Catherine who, we must not forget, is still undergoing gruelling preventative chemotherapy treatment as well as continuing to recuperate from her initial abdominal surgery in January - the seriousness of which should not be underestimated by anyone.

‘Obviously it’s been an important day [today] and one that has huge resonance with the prince in terms of his own environmental commitments, but I think you can expect to see the Prince undertake engagements at a similar pace to February and March,’ a source stresses.

‘The prince has always made clear that he wants to balance his commitment to public service and duty with supporting his family at this time, and he will continue to find a way to do that. ‘

Fortunately in this William has his wife’s backing, wholeheartedly.

‘Absolutely, it’s important to both of them, actually,’ my source adds.

‘June is an incredibly busy time ceremonially and the princess will want him to play his part as well.

‘They share that same sense of commitment and service.’

While there are many hurdles yet to be crossed, it is clear that William and Catherine are finding their way through them, together.