"Yes, he was raising money for his charity, but Joost just wanted to spend some time with us, so we went out to a bit of a lodge just outside Johannesburg and spent two or three days with him.
"In the early stages, he was OK, but two years ago, he was confined to a wheelchair, struggling to hold his head and needed a neck brace.
"Things weren't looking that great at that stage and it was really difficult to see him like that, when we knew what he was like as a player on the rugby field. Both George and I were pleased we went over and had that great opportunity to spend some personal time with him.
"Throughout the period that Joost had his motor neurone and he was doing a wonderful job with his J9 foundation ... that again was typical of the man that he didn't put himself first."
Over his 10-year Springbok career, van der Westhuizen played 89 tests, helping his team to victory at the 1995 World Cup over New Zealand and the 1998 Tri-Nations. He contested three World Cups, and was inducted into the International Rugby Hall of Fame and World Rugby Half of Fame.
One of the most iconic images of his career was his tackle on a rampaging Jonah Lomu during that historic 1995 World Cup final. Both are now gone within 15 months of each other.
Van der Westhuizen was first diagnosed with motor neurone in 2011 and given only months to survive.
"He had quite an aggressive form of the disease, however he fought and battled for six years, which not only typified him as a person, but also the type of rugby player and fighter he was," reflected Marshall. "He was the ultimate competitor ... not many scrumhalves aren't, I guess.
"Joost just had a quiet determination about him. He wasn't as vocal as the likes of George Gregan or Matt Dawson when I was playing against him.
"He just had an ability, on the flip of a coin, to change a game. Joost could have moments in games where he was off and not only quiet, he would make the odd mistake.
"But that didn't happen over a continuous period of 80 minutes, all of a sudden, through a 20-minute period, he could change the game on his own. A player like that was someone you could never underestimate, was always dangerous."
Marshall claimed that van der Westhuizen was, at his peak, the best rugby player on the planet.
"Players like that don't come along very often," he said. "I always felt, when he was on the field, even if we were up by 20 points ...
"I remember a game in Durban, where we were dominating the game, but he was the catalyst for turning the game around and we ended up losing on a controversial try. Joost vanwesthuizen in 20 minutes of that game, that's what the man was all about."