Signed by Alex McLeish in January 2004, De Boer joined twin brother Ronald at Ibrox but was not able to prevent Rangers enduring their second trophyless season in four years. By the end of the campaign, Celtic had finished the season as champions, 17 points clear of their greatest rivals, and had also knocked Rangers out of the Scottish Cup on their way to concluding a domestic double.
De Boer played twice at Celtic Park during that period and lost both games. It is with a certain irony that he cursed the genius of Henrik Larsson - a scorer in one of those games and a regular scourge of Rangers - while sat in the stadium's No.7 lounge yesterday. Had he elected to take a wander around the room rather than heading straight for the exit, he would have noticed pictures of the Swede - as well as of Jimmy Johnstone - beaming down from every corner, the room an homage to the pair's consistent brilliance in a Celtic shirt.
"Of course it was a great atmosphere at Celtic Park because of the rivalry between the clubs," De Boer recalled. "I had quite a good feeling about it but I played against Henrik Larsson and he was a real pain in the ass at that time for Rangers. I had him under control but a free kick landed just at his feet and I thought it was quite a lucky goal. There was also another game and we lost in the last minute to Celtic again. For me the atmosphere is still in my mind, it was fantastic, the people shouting at you. For me it was a great adventure."
Now an opportunity has presented itself for De Boer to belatedly make up for past disappointments. It is Champions League football that has brought him back to Glasgow, the Ajax manager looking to bring further European success to a club whose history and heritage places it firmly among the elite. Three consecutive Eredivisie league championships testify that De Boer is a more than capable young coach but it is on the European stage that a club like Ajax will always be judged. The resources are not what they once were but the demands on the Amsterdamers are still the same.
That much was made clear by the hundreds that braved the pouring rain in Glasgow last night to take their place in the main stand and watch their heroes train. Thousands more will fill a corner of Celtic Park this evening as Ajax look to improve their chances of reaching the last 16 of the Champions League by beating their hosts. Having finished third in the group stage for three seasons running, the presence of Barcelona and AC Milan this time around would suggest third will be the best Ajax can hope for again but De Boer is not entirely without hope.
He praised Celtic for what they have achieved in recent seasons - "they are an example of how to run a club" - and there are similarities to the tasks facing both he and counterpart Neil Lennon. Like the Celtic manager, De Boer lost key players during the summer because the price was too good for a club of Ajax's size to turn down; Christian Eriksen went to Tottenham Hotspur for £12m, Toby Alderweireld to Atletico Madrid for £6m.
That has left De Boer with a youthful squad; his oldest player in Saturday's game against Twente Enschede just 24 years old. Such a young side can offer great energy but there is also a question mark over just how they will respond to a raucous Celtic Park at its noisiest. Ajax have yet to win an away game in any competition this season.
"For me our players have to enjoy this kind of atmosphere," De Boer said. "When you are young you want to play in this kind of stadium with this kind of atmosphere. It can only give you more adrenaline in your body to perform. If you are worse than your normal level then maybe you're not good enough to play at this level. Of course, you can be nervous when the referee starts the game but you must get rid of all the nerves and enjoy a great stadium and great pitch."
Frank was always the more modest of the twins - Ronald was never a great one for diplomacy during his time at Rangers - and there was an appreciation that, while Ajax will continue to strive for second, making sure his team finish third and parachute into the Europa League after Christmas, should also be considered.
"We want to play in Europe after the winter break so we really want to win or at least we want to have a draw," De Boer said. "That's very important. If we lose it will be very difficult but that goes for both teams. Of course, we would prefer to win the game. If we want the potential to finish in second place then the best thing is to win. That might also put us in a good position for third place.
"To lose is the worst option but a draw could maybe be enough because in two weeks' time we have Celtic in the Amsterdam ArenA. If we lose this game it gives Celtic a big advantage so we want to get three points from Celtic Park if we can."