Spurs and Fulham confirmed the transfer of Dembele for a fee understood to be in the region of ?15million after the forward passed a medical and agreed a five-year contract.
The Belgian international midfielder added on Twitter: "Happy to confirm I signed a new contract with Tottenham FC! I would like to thank all the Fulham fans for their support! You were amazing."
The news followed a declaration by Hamburg that they would do everything possible to re-sign Van der Vaart from Tottenham before the transfer window closed. Van der Vaart has been strongly linked with a return to his former club but the Bundesliga side's chairman, Carl-Edgar Jarchow, has admitted time is running out to convince Spurs to sell.
"There is not a lot of time - it is really up to Tottenham Hotspur," he told Deutsche Presse-Agentur. "If we have a chance to sign him, we will do everything we can to make that happen."
That opportunity could present itself now Tottenham have successfully begun to sign some of their own targets during what looks set to be another frantic final 48 hours of a summer transfer window at White Hart Lane.
As well as triggering what was reportedly Dembele's Fulham release clause, new manager Villas-Boas has renewed the interest he showed while Chelsea boss in Shakhtar Donetsk forward Willian, who could fill the void left by the departure of Luka Modric.
Shakhtar chief executive Sergei Palkin today claimed he had rejected a bid of just under £12million for the Brazilian and that Tottenham chairman Daniel Levy had also made an enquiry about two other players.
"Mr Levy, the chairman of Tottenham Hotspur FC, personally flew to Donetsk to negotiate over Willian," Palkin told his club's official website, www.shakhtar.com. But his latest offer was 15 million euros, which we, of course, did not accept.
"Levy, by the way, hinted that besides Willian, Villas-Boas was interested in Douglas Costa and Fernandinho, but he mentioned that just casually, without any specifics."
Source: PA
Source: PA