Alderweireld enjoyed a successful season on loan with Saints from Atletico Madrid and had been expected to complete a full-time switch before Spurs gazumped their Premier League rivals in a move which has left the south coast club seeking legal advice.
Alderweireld admits he is aware the furore his decision has caused.
“I understand that there is some disappointment,” the Belgium defender told the London Evening Standard.
“I have sent a text message to Ronald and thanked him for a great year. He gave me a lot of confidence and made me a better footballer.
“I gave 100 per cent for Southampton and wish everyone luck for next season.”