"The timing is right now, we are both very, very happy," Prince William said, laughing off questions about what took him so long to propose.
He also joked that he "didn't know it was a race".
Kate Middleton, for her part, said it was a "natural step for both of us". "We had spoken about our future," she explained.
It wasn't a race of course. But their relaxed and happy demeanour during the engagement announcement belies how testing life as his unofficial consort must have been for Kate.
Only now seeing her radiating joy that the next stage of her life as the Prince's fiancée is beginning, can anyone imagine the strain she has been under.
There was some hint of the difficulties in their joint interview when she described her future husband as "very supportive of me in good times and also for the bad times".
"Over the years he's looked after me and treated me very well as the great and loving boyfriend he is".
Those bad times included scrutiny of her family and everything they did, while being unable to comment.
ON HER WORK
Detractors opined that her roles, first with Jigsaw, and then for her parents' Party Pieces company did not constitute proper work for someone of her relatively privileged background and education.
Able to speak out at last this week, she said of the accusations: “I know I have been working very hard for the family business”. “Sometimes those days are long days".
"You can only be true to yourself and you sort of have to ignore a lot of what is said, obviously take it on board, but you have to be yourself.
In 2007, with their temporary split when her royal beau decided, as he explained, that he needed "some space", came the hardest trial of all.
"I, at the time, wasn't very happy about it but actually it made me a stronger person. You find out things about yourself that maybe you hadn’t realised," said the 28-year-old.
"You can get quite consumed by a relationship when you are younger.
"I really valued that time, for me as well … looking back on it".
Not only did the Berkshire girl face a life without the love of the young man she had adored for so long, she did so in the full glare of the media spotlight.
Whatever private heartache she felt, there was no hiding away.
Resilient Kate rallied, showing the inner steel behind the perfectly groomed exterior, serving up a smile whenever photographers were around - as they were in their scores, camped round her family home and regular haunts.
Her parents and siblings, Pippa and James undoubtedly helped her cope. In tribute to them she said: "They've been great over the years - helping me with difficult times".
Most importantly she resisted any temptation to comment or pour her heart, keeping steadfastly loyal to the Prince and his family.
The separation only served to underline how pivotal she was in his life. But while their relationship started up again and they were increasingly close, Kate was still outside the royal fold.
Not yet an official partner, she spent important occasions like Christmases apart from William, while he joined the royal clan at Sandringham.
Incidentally she had not been a guest when Prince Charles wed the Duchess of Cornwall in 2005 either.